Termbank
  1. A
    1. API Blueprint
    2. Addressability
    3. Ajax
    4. Anonymous Function
    5. App Context
  2. B
    1. Blueprint
    2. Business Logic
  3. C
    1. CORS
    2. Callback
    3. Client
    4. Column
    5. Column Attribute
    6. Connectedness
    7. Control
  4. D
    1. DOM
    2. Database Schema
  5. E
    1. Element
    2. Entry Point
  6. F
    1. Fixture
    2. Flask App
    3. Foreign Key
  7. G
    1. Generic Client
  8. H
    1. HTTP Method
    2. HTTP Request
    3. Header
    4. Host Part
    5. Hypermedia
  9. I
    1. Idempotent
    2. Instance Folder
  10. J
    1. JSON
    2. JSON Schema
  11. L
    1. Link Relation
  12. M
    1. MIME Type
    2. Migration
    3. Model Class
  13. N
    1. Namespace
  14. O
    1. ORM
  15. P
    1. Primary Key
    2. Profile
  16. Q
    1. Query
    2. Query Parameter
  17. R
    1. Regular Expression
    2. Request
    3. Request Body
    4. Request Object
    5. Resource
    6. Resource Class
    7. Resource Representation
    8. Response
    9. Response Body
    10. Response Object
    11. Rollback
    12. Routing
    13. Route
      Routing
    14. Row
  18. S
    1. SQL
    2. Serialization
    3. Static Content
  19. T
    1. Table
    2. Test Setup
    3. Test Teardown
  20. U
    1. URI
    2. URL Template
    3. Uniform Interface
    4. Unique Constraint
  21. V
    1. View Function
    2. Virtualenv
  22. W
    1. Web API
Completed: / exercises

Extra Chapter: Managing Relations

There is a topic that comes up in many projects but was not covered in the MusicMeta API example: managing relationships between existing
resources
. The scope of the API only included resources that have static relations with each other - i.e. relationships that do not change over time. We can however easily come up with another set of data for the API that does need assignment of existing resources to relationships with each other: the members of bands change over time. This is also a many-to-many relationship because there's no rule against being in multiple bands.

Specification

In order to accomplish this, we need to introduce a new
model
to our database: Musician. Also, because musician's relationship with artist is many-to-many, a relationship table is required. These are shown below.
artist_membership_table = db.Table("membership",
    db.Column("musician_id", db.Integer, db.ForeignKey("musician.id"), primary_key=True),
    db.Column("artist_id", db.Integer, db.ForeignKey("artist.id"), primary_key=True)
)

class Musician(db.Model):

    id = db.Column(db.Integer, primary_key=True)
    unique_name = db.Column(db.String, nullable=False, unique=True)
    first_name = db.Column(db.String)
    last_name = db.Column(db.String, nullable=False)
    
    artists = db.relationship("Artist", secondary=artist_membership_table)

    def __repr__(self):
        return "{}, {} <{}>".format(self.last_name, self.first_name, self.id)
We would also add the following relationship attribute to the Artist model:
    members = db.relationship("Musician", secondary=artist_membership_table)
Managing memberships on the code level is quite straightforward: the relationships work just like Python lists so we can append and remove members from the artist end rather effortlessly. The real question is how this should be managed through a RESTful API. We don't really want to do this with a PUT request although it would be possible to have an array of musician unique names as an attribute in a
JSON
request body
. This is awkward because we will have to check through the entire submitted list for differences, or delete all of the existing relationships and then create everything anew. This is not a significant performance hit in our case because the number of musicians per artist is relatively small. However, we have better ways to do it.

Solution 1: Relationship Resources

A resource-oriented solution is to represent the connection between two resources as a resource itself. This is a special case of a resource that doesn't contain any data but it is instead meaningful just because it exists. This relationship resource can be routed to e.g.
/api/artists/{artist_unique_name}/members/{musician_unique_name}/
The existence of a resource fitting this
URL template
means that the musician identified by their unique name is a member in the artist identified by its unique name. But how should this type of resource be created? There are two options:
  1. by POST request to /api/artists/{artist_unique_name}/members/
  2. by PUT request to /api/artists/{artist_unique_name}/members/{musician_unique_name}/
So far we've been emphasizing the creation of new resources with POST. However, creating resources with PUT is also valid. It's simply not usually recommended because in order to make a PUT request, the client needs to know the
URI
of the resource beforehand. For example in our case, if the client was tryign to add a second artist with a name that's already taken, its best guess might end up replacing the existing artist's information with the new one's. The creation of a relationship resource is different: the URI is formed of existing unique names so the client actually does have a way of knowing what the URI should be. Since you should already know how to do this with POST, we're going to show how to use PUT.
As usual we need to inform the client about this action by adding a
hypermedia
control. This can be in the artist resource, or in the members resource should we make one. The control uses an href template with an attached
schema
that tells how to form the final URI. Much like the album sorting control we did, except this time the URL variable is in the address itself, not in the
query string
.
{
    "mumeta:add-member": {
        "href": "/api/artists/scandal/members/{musician}/",
        "title": "Add a member to this artist",
        "isHrefTemplate": true,
        "method": "PUT",
        "schema": {
            "properties": {
                "musician": {
                    "type": "string",
                    "description": "Musician's unique name"
                }
            }
        }
    }
}
Removing a member becomes a very simple interaction: simply send DELETE to the resource that represents the relationship. For our resource representation the following control can be attached to each member.
{
    "mumeta:remove-member": {
        "href": "/api/artists/scandal/members/ogawa_tomomi/",
        "title": "Remove this member from the artist",
        "method": "DELETE"
    }
}
There is actually no reason for the relationship resource to support GET - there's no data there so there's very little reason for clients to retrieve it.

Solution 2: PATCH Method

Alternatively the problem can be solved using the HTTP PATCH method. This method has not been introduced earlier because it is not as widely used. Mostly because its definition is more vague - a client developer cannot infer what a PATCH method is supposed to do like they can with PUT. The PATCH method is used to send a representation of changes to the resource. The correct way of representing changes depends on the API which greatly reduces the uniformity of this
HTTP method
. Please note that PATCH should not be treated as a partial PUT. If all you are doing is replacing some attribute values, you should always use PUT because it doesn't need any explanation, and because it is
idempotent
. Filling the unchanged values into the request is not a big deal for clients.
What PATCH should be used for is to describe changes that would be inconvenient to implement with PUT. Like assigning new members to a group. However, the easiest way to illustrate the use of PATCH and how it differs from PUT is incrementing a counter. Let's assume a resource that has an integer attribute simply called "counter". A PATCH
request body
to increment a counter by one (without knowing its current value) could be:
{
    "operation": "increment",
    "attribute": "counter"
}
This is a format we just literally cooked up so it is definitely not very universal - and this is the problem with PATCH. There is a standard propsal for PATCH documents called JSON Patch which should help us a little bit. The JSON Patch version of the same operation is not quite as illustrative, but should be pretty clear:
{
    "op": "add", 
    "path": "/counter",
    "value": 1
}
The reverse operation is "remove". We can use this format to represent addition and removal of members, e.g. to add a member:
{
    "op": "add",
    "path": "/members",
    "value": "ogawa_tomomi"
}
and to remove:
{
    "op": "remove",
    "path": "/members",
    "value": "ogawa_tomomi"
}
In terms of
hypermedia
controls we can combine the two into one control. This is the description that should be dropped into the artist resource or the members resource (if one is added - the example uses the artist resource).
{
    "mumeta:manage-members": {
        "href": "/api/artists/scandal/",
        "title": "Add or remove members from this artist",
        "method": "PATCH",
        "schema": {
            "type": "object",
            "properties": {
                "op": {
                    "description": "Add or remove members"
                    "type": "string",
                    "enum": ["add", "remove"]
                },
                "path":{
                    "description": "Affected attribute",
                    "type": "string",
                    "default": "/members",
                    "enum": ["/members"]
                },
                "value": {
                    "description": "Unique name of the musician to add/remove",
                    "type": "string"
                }
            }
        }
    }
}
Note that although the path attribute has only one possible value the client still has to send it since we should follow the JSON Patch standard in our validation. It would also be possible to describe two different controls where the op attribute is also fixed to separate the adding and removing of members.

Relationships with Data

Actually there is one more thing to discuss about this topic. The examples above are for a simple case where the relationship between artist and musician simply exists or doesn't. However for a real use case it makes more sense to include time spans because sometimes members come and go. In this case it definitely makes more sense to turn the relationship itself into a
resource
.

Changes to Models

When the relationship itself contains data this also means that in the backend side we should turn the relationship table into a proper
model
.
class ArtistMembership(db.Model):
    __tablename__ = "membership"
    
    musician_id = db.Column(db.Integer, db.ForeignKey("musician.id", ondelete="CASCADE"), primary_key=True)
    artist_id = db.Column(db.Integer, db.ForeignKey("artist.id", ondelete="CASCADE"), primary_key=True)
    joined = db.Column(db.Date, nullable=False)
    left = db.Column(db.Date, nullable=True)
    
    musician = db.relationship("Musician", back_populates="artists")
    artist = db.relationship("Artist", back_populates="members")
We've set the __tablename__ attribute this time because we want the name to match the table that we created previously instead of using the class name in lowercase. After changing the association table, the Artist and Musician models no longer refer to each other directly with the relationship's secondary attribute. Instead they both have a relationship to the association model but no foreign key to it. So for change the relationship attributes
    # for Musician model
    artists = db.relationship("ArtistMembership", back_populates="artist", cascade="all,delete-oprhan")
    
    # for Artist model
    members = db.relationship("ArtistMembership", back_populates="musician", cascade="all,delete-oprhan")
Now in order to add a member to an artist we have to create the membership object in addition to the musician which adds an extra step:
In [1]: from app import db, Musician, ArtistMembership, Artist
In [2]: import datetime
In [3]: member = Musician(unique_name="ogawa_tomomi", first_name="Tomomi", last_name="Ogawa")
In [4]: artist = Artist.query.filter_by(unique_name="scandal").first()
In [5]: membership = ArtistMembership(joined=artist.formed, musician=member)
In [6]: artist.members.append(membership)
In [7]: db.session.commit()
And in order to access a member through the relationship:
In [8]: artist.members[0].musician.first_name
Out[8]: "Tomomi"

Changes to Resources

This time it's definitely correct to treat memberships as
resources
. Whether it should support GET or not is up to preference. Overall it will mostly the same as the first solution we had to the previous problem. However since the resource now contains data, PUT could do two things: create a new one or edit an existing one (e.g. to update the membership with a left attribute when someone leaves). Another problem with using PUT in this case is that for the first time Mason lets us down a bit. In Mason, the schema attribute of a control is used to describe both
request body
and the parameters for a
URL template
. The problem is we would need both, but there is no way to indicate what part of the schema describes the request body and what are parameters. Sure, clients can parse it from the href attribute but the schema itself cannot be used to validate the request body if it also contains parameters.
So this time the better route is to make the membership list a resource (at /api/artists/{artist}/members/) that supports GET and POST, where the POST method is used for adding new members. Removal of members is still handled by DELETE to the membership resource like previously. We're not going to show the entire membership list resource, just the control that adds a new member.
{
    "mumeta:add-member": {
        "href": "/api/artists/{artist}/members/",
        "title": "Add a new member to this artist.",
        "method": "POST",
        "schema": {
            "type": "object",
            "properties": {
                "first_name": {
                    "type": "string",
                    "description": "The members's first name"
                },
                "last_name": {
                    "type": "string",
                    "description": "The members's last name"
                },
                "joined": {
                    "description": "Date joined",
                    "type": "string",
                    "pattern": "^[0-9]{4}-[01][0-9]-[0-3][0-9]$",
                    "format": "date"
                },
                "left": {
                    "description": "Date left",
                    "type": "string",
                    "pattern": "^[0-9]{4}-[01][0-9]-[0-3][0-9]$",
                    "format": "date"
                },
            },
            "required": ["last_name", "joined"]
        }
    }
}
?
API Blueprint is a description language for REST APIs. Its primary categories are resources and their related actions (i.e. HTTP methods). It uses a relatively simple syntax. The advantage of using API Blueprint is the wide array of tools available. For example Apiary has a lot of features (interactive documentation, mockup server, test generation etc.) that can be utilized if the API is described in API Blueprint.
Another widely used alteranative for API Blueprint is OpenAPI.
Addressability is one of the key REST principles. It means that in an API everything should be presented as resources with URIs so that every possible action can be given an address. On the flipside this also means that every single address should always result in the same resource being accessed, with the same parameters. From the perspective of addressability, query parameters are part of the address.
Ajax is a common web technique. It used to be known as AJAX, an acronym for Asynchronous Javascript And XML but with JSON largely replacing XML, it become just Ajax. Ajax is used in web pages to make requests to the server without a page reload being triggered. These requests are asynchronous - the page script doesn't stop to wait for the response. Instead a callback is set to handle the response when it is received. Ajax can be used to make a request with any HTTP method.
  1. Description
  2. Examples
Anonymous functions are usually used as in-place functions to define a callback. They are named such because they are defined just like functions, but don't have a name. In JavaScript function definition returns the function as an object so that it can e.g. passed as an argument to another function. Generally they are used as one-off callbacks when it makes the code more readable to have the function defined where the callback is needed rather than somewhere else. A typical example is the forEach method of arrays. It takes a callback as its arguments and calls that function for each of its members. One downside of anonymous functions is that they function is defined anew every time, and this can cause significant overhead if performed constantly.
  1. Description
  2. Example
In Flask application context (app context for short) is an object that keeps tracks of application level data, e.g. configuration. You always need to have it when trying to manipulate the database etc. View functions will automatically have app context included, but if you want to manipulate the database or test functions from the interactive Python console, you need to obtain app context using a with statement.
Blueprint is a Flask feature, a way of grouping different parts of the web application in such a way that each part is registered as a blueprint with its own root URI. Typical example could be an admin blueprint for admin-related features, using the root URI /admin/. Inside a blueprint, are routes are defined relatively to this root, i.e. the route /users/ inside the admin blueprint would have the full route of /admin/users/.
Defines how data is processed in the application
Cross Origin Resource Sharing (CORS) is a relaxation mechanism for Same Origin Policy (SOP). Through CORS headers, servers can allow requests from external origins, what can be requested, and what headers can be included in those requests. If a server doesn't provide CORS headers, browsers will browsers will apply the SOP and refuse to make requests unless the origin is the same. Note that the primary purpose of CORS is to allow only certain trusted origins. Example scenario: a site with dubious script cannot just steal a user's API credentials from another site's cookies and make requests using them because the APIs CORS configuration doesn't allow requests from the site's origin. NOTE: this is not a mechanism to protect your API, it's to protect browser users from accessing your API unintentionally.
Callback is a function that is passed to another part of the program, usually as an argument, to be called when certain conditions are met. For instance in making Ajax requests, it's typical to register a callback for at least success and error situations. A typical feature of callbacks is that the function cannot decide its own parameters, and must instead make do with the arguments given by the part of the program that calls it. Callbacks are also called handlers. One-off callbacks are often defined as anonymous functions.
Piece of software that consumes or utilizes the functionality of a Web API. Some clients are controlled by humans, while others (e.g. crawlers, monitors, scripts, agents) have different degree of autonomy.
In databases, columns define the attributes of objects stored in a table. A column has a type, and can have additional properties such as being unique. If a row doesn't conform with the column types and other restrictions, it cannot be inserted into the table.
  1. Description
  2. Common keywords
In object relational mapping, column attributes are attributes in model classes that have been initialized as columns (e.g. in SQLAlchemy their initial value is obtained by initializing a Column). Each of these attributes corresponds to a column in the database table (that corresponds with the model class). A column attribute defines the column's type as well as additional properties (e.g. primary key).
Connectedness is a REST principle particularly related to hypermedia APIs. It states that there for each resource in the API, there must exist a path from every other resource to get there by following hypermedia links. Connectedness is easiest to analyze by creating an API state diagram.
  1. Description
  2. Example
A hypermedia control is an attribute in a resource representation that describes a possible action to the client. It can be a link to follow, or an action that manipulates the resource in some way. Regardless of the used hypermedia format, controls include at least the URI to use when performing the action. In Mason controls also include the HTTP method to use (if it's not GET), and can also include a schema that describes what's considered valid for the request body.
Document Object Model (DOM) is an interface through which Javascript code can interact with the HTML document. It's a tree structure that follows the HTML's hierarchy, and each HTML tag has its own node. Through DOM manipulation, Javascript code can insert new HTML into anywhere, modify its contents or remove it. Any modifications to the DOM are updated into the web page in real time. Do note that since this is a rendering operation, it's very likely one of the most costly operations your code can do. Therefore changing the entire contents of an element at once is better than changing it e.g. one line at a time.
Database schema is the "blueprint" of the database. It defines what tables are contained in the database, and what columns are in each table, and what additional attributes they have. A database's schema can be dumped into an SQL file, and a database can also be created from a schema file. When using object relational mapping (ORM), the schema is constructed from model classes.
In HTML element refers to a single tag - most of the time including a closing tag and everything in between. The element's properties are defined by the tag, and any of the properties can be used to select that element from the document object model (DOM). Elements can contain other elements, which forms the HTML document's hierarchy.
For APIs entry point is the "landing page" of the API. It's typically in the API root of the URL hierarchy and contains logical first steps for a client to take when interacting with the API. This means it typically has one or more hypermedia controls which usually point to relevant collections in the API or search functions.
In software testing, a fixture is a component that satisfies the preconditions required by tests. In web application testing the most common role for fixtures is to initialize the database into a state that makes testing possible. This generally involves creating a fresh database, and possibly populating it with some data. In this course fixtures are implemented using pytest's fixture architecture.
  1. Description
  2. Creating DB
  3. Starting the App
This term contains basic instructions about setting up and running Flask applications. See the term tabs "Creating DB" and "Starting the App". For all instructions to work you need to be in the folder that contains your app.
In database terminology, foreign key means a column that has its value range determined by the values of a column in another table. They are used to create relationships between tables. The foreign key column in the target table must be unique.
For most hypermedia types, there exists a generic client. This is a client program that constructs a navigatable user interface based on hypermedia controls in the API, and can usually also generate data input forms. The ability to use such clients for testing and prototyping is one of the big advantages of hypermedia.
HTTP method is the "type" of an HTTP request, indicating what kind of an action the sender is intending to do. In web applications by far the most common method is GET which is used for retrieving data (i.e. HTML pages) from the server. The other method used in web applications is POST, used in submitting forms. However, in REST API use cases, PUT and DELETE methods are also commonly used to modify and delete data.
HTTP request is the entirety of the requets made by a client to a server using the HTTP protocol. It includes the request URL, request method (GET, POST etc.), headers and request body. In Python web frameworks the HTTP request is typically turned into a request object.
Headers are additional information fields included in HTTP requests and responses. Typical examples of headers are content-type and content-length which inform the receiver how the content should be interpreted, and how long it should be. In Flask headers are contained in the request.headers attribute that works like a dictionary.
Host part is the part of URL that indicates the server's address. For example, lovelace.oulu.fi is the host part. This part determines where (i.e. which IP address) in the world wide web the request is sent.
In API terminology hypermedia means additional information that is added on top of raw data in resource representations. It's derived from hypertext - the stuff that makes the world wide web tick. The purpose of the added hypermedia is to inform the client about actions that are available in relation to the resource they requested. When this information is conveyed in the representations sent by the API, the client doesn't need to know how to perform these actions beforehand - it only needs to parse them from the response.
An idempotent operation is an operation that, if applied multiple times with the same parameters, always has the same result regardless of how many times it's applied. If used properly, PUT is an idempotent operation: no matter how many times you replace the contents of a resource it will have the same contents as it would have if only one request had been made. On the other hand POST is usually not idempotent because it attempts to create a new resource with every request.
Instance folder is a Flask feature. It is intended for storing files that are needed when running the Flask application, but should not be in the project's code repository. Primary example of this is the prodcution configuration file which differs from installation to installation, and generally should remain unchanged when the application code is updated from the repository. The instance path can be found from the application context: app.instance_path. Flask has a reasonable default for it, but it can also be set manually when calling Flask constuctor by adding the instance_path keyword argument. The path should be written as absolute in this case.
  1. Description
  2. Serializing / Parsing
JavaScript Object Notation (JSON) is a popular document format in web development. It's a serialized representation of a data structure. Although the representation syntax originates from JavaScript, It's almost identical to Python dictionaries and lists in formatting and structure. A JSON document conists of key-value pairs (similar to Python dictionaries) and arrays (similar to Python lists). It's often used in APIs, and also in AJAX calls on web sites.
JSON schema is a JSON document that defines the validity criteria for JSON documents that fall under the schema. It defines the type of the root object, and types as well as additional constraints for attributes, and which attributes are required. JSON schemas serve two purposes in this course: clients can use them to generate requests to create/modify resources, and they can also be used on the API end to validate incoming requests.
  1. Description
  2. Common MIME types
MIME type is a standard used for indicating the type of a document.In web development context it is placed in the Content-Type header. Browsers and servers the MIME type to determine how to process the request/response content. On this course the MIME type is in most cases application/json.
Database migration is a process where an existing database is updated with a new database schema. This is done in a way that does not lose data. Some changes can be migrated automatically. These include creation of new tables, removal of columns and adding nullable columns. Other changes often require a migration script that does the change in multiple steps so that old data can be transformed to fit the new schema. E.g. adding a non-nullable column usually involves adding it first as nullable, then using a piece of code to determine values for each row, and finally setting the column to non-nullable.
  1. Description
  2. Example
In ORM terminology, a model class is a program level class that represents a database table. Instances of the class represent rows in the table. Creation and modification operations are performed using the class and instances. Model classes typically share a common parent (e.g. db.Model) and table columns are defined as class attributes with special constuctors (e.g. db.Column).
  1. Description
  2. Example
In API terminology, namespace is a prefix for names used by the API that makes them unique. The namespace should be a URI, but it doesn't have to be a real address. However, usually it is convenient to place a document that described the names within the namespace into the namespace URI. For our purposes, namespace contains the custom link relations used by the API.
Object relational mapping is a way of abstracting database use. Database tables are mapped to programming language classes. These are usually called models. A model class declaration defines the table's structure. When rows from the database table are fetched, they are represented as instances of the model class with columns as attributes. Likewise new rows are created by making new instances of the model class and committing them to the database. This course uses SQLAlchemy's ORM engine.
In database terminology primary key refers to the column in a table that's intended to be the primary way of identifying rows. Each table must have exactly one, and it needs to be unique. This is usually some kind of a unique identifier associated with objects presented by the table, or if such an identifier doesn't exist simply a running ID number (which is incremented automatically).
Profile is metadata about a resource. It's a document intended for client developers. A profile gives meaning to each word used in the resource representation be it link relation or data attribute (also known as semantic descriptors). With the help of profiles, client developers can teach machine clients to understand resource representations sent by the API. Note that profiles are not part of the API and are usually served as static HTML documents. Resource representations should always contain a link to their profile.
In database terminology, query is a command sent to the database that can fetch or alter data in the database. Queries use written with a script-like language. Most common is the structured query language (SQL). In object relational mapping, queries are abstracted behind Python method calls.
  1. Description
  2. Example
Query parameters are additional parameters that are included in a URL. You can often see these in web searches. They are the primary mechanism of passing arbitrary parameters with an HTTP request. They are separated from the actual address by ?. Each parameter is written as a key=value pair, and they are separated from each other by &. In Flask applications they can be found from request.args which works like a dictionary.
  1. Description
  2. Examples
Regular expressions are used in computing to define matching patterns for strings. In this course they are primarily used in validation of route variables, and in JSON schemas. Typical features of regular expressions are that they look like a string of garbage letters and get easily out of hand if you need to match something complex. They are also widely used in Lovelace text field exercises to match correct (and incorrect) answers.
In this course request referes to HTTP request. It's a request sent by a client to an HTTP server. It consists of the requested URL which identifies the resource the client wants to access, a method describing what it wants to do with the resource. Requests also include headers which provide further context information, and possihby a request body that can contain e.g. a file to upload.
  1. Description
  2. Accessing
In an HTTP request, the request body is the actual content of the request. For example when uploading a file, the file's contents would be contained within the request body. When working with APIs, request body usually contains a JSON document. Request body is mostly used with POST, PUT and PATCH requests.
  1. Description
  2. Getting data
Request object is related to web development frameworks. It's a programming language object representation of the HTTP request made to the server. It has attributes that contain all the information contained within the request, e.g. method, url, headers, request body. In Flask the object can be imported from Flask to make it globally available.
in RESTful API terminology, a resource is anything that is interesting enough that a client might want to access it. A resource is a representation of data that is stored in the API. While they usually represent data from the database tables it is important to understand that they do not have a one-to-one mapping to database tables. A resource can combine data from multiple tables, and there can be multiple representations of a single table. Also things like searches are seen as resources (it does, after all, return a filtered representation of data).
Resource classes are introduced in Flask-RESTful for implementing resources. They are inherited from flask_restful.Resource. A resource class has a view-like method for each HTTP method supported by the resource (method names are written in lowercase). Resources are routed through api.add_resource which routes all of the methods to the same URI (in accordance to REST principles). As a consequence, all methods must also have the same parameters.
In this course we use the term representation to emphasize that a resource is, in fact, a representation of something stored in the API server. In particular you can consider representation to mean the response sent by the API when it receives a GET request. This representation contains not only data but also hypermedia controls which describe the actions available to the client.
In this course response refers to HTTP response, the response given by an HTTP server when a request is made to it. Reponses are made of a status code, headers and (optionally) response body. Status code describes the result of the transaction (success, error, something else). Headers provide context information, and response body contains the document (e.g. HTML document) returned by the server.
Response body is the part of HTTP response that contains the actual data sent by the server. The body will be either text or binary, and this information with additional type instructions (e.g. JSON) are defined by the response's Content-type header. Only GET requests are expected to return a response body on a successful request.
Response object is the client side counterpart of request object. It is mainly used in testing: the Flask test client returns a response object when it makes a "request" to the server. The response object has various attributes that represent different parts of an actual HTTP response. Most important are usually status_code and data.
In database terminology, rollback is the cancellation of a database transaction by returning the database to a previous (stable) state. Rollbacks are generally needed if a transaction puts the database in an error state. On this course rollbacks are generally used in testing after deliberately causing errors.
  1. Description
  2. Routing in Flask
  3. Reverse routing
  4. Flask-RESTful routing
URL routing in web frameworks is the process in which the framework transforms the URL from an HTTP request into a Python function call. When routing, a URL is matched against a sequence of URL templates defined by the web application. The request is routed to the function registered for the first matching URL template. Any variables defined in the template are passed to the function as parameters.
In relational database terminology, row refers to a single member of table, i.e. one object with properties that are defined by the table's columns. Rows must be uniquely identifiable by at least one column (the table's primary key).
SQL (structured query language) is a family of languages that are used for interacting with databases. Queries typically involve selecting a range of data from one or more tables, and defining an operation to perform to it (such as retrieve the contents).
Serialization is a common term in computer science. It's a process through which data structures from a program are turned into a format that can be saved on the hard drive or sent over the network. Serialization is a reversible process - it should be possible to restore the data structure from the representation. A very common serialization method in web development is JSON.
In web applications static content refers to content that is served from static files in the web server's hard drive (or in bigger installations from a separate media server). This includes images as well as javascript files. Also HTML files that are not generated from templates are static content.
In database terminology, a table is a collection of similar items. The attributes of those items are defined by the table's columns that are declared when the table is created. Each item in a table is contained in a row.
In software testing, test setup is a procedure that is undertaken before each test case. It prepares preconditions for the test. On this course this is done with pytest's fixtures.
In software testing, test teardown is a process that is undertaken after each test case. Generally this involves clearing up the database (e.g. dropping all tables) and closing file descriptors, socket connections etc. On this course pytest fixtures are used for this purpose.
Universal resource identifier (URI) is basically what the name says: it's a string that unambiguously identifies a resource, thereby making it addressable. In APIs everything that is interesting enough is given its own URI. URLs are URIs that specify the exact location where to find the resource which means including protocol (http) and server part (e.g. lovelace.oulu.fi) in addition to the part that identifies the resource within the server (e.g. /ohjelmoitava-web/programmable-web-project-spring-2019).
  1. Description
  2. Type converters
  3. Custom converters
URL template defines a range of possible URLs that all lead to the same view function by defining variables. While it's possible for these variables to take arbitrary values, they are more commonly used to select one object from a group of similar objects, i.e. one user's profile from all the user profiles in the web service (in Flask: /profile/<username>. If a matching object doesn't exist, the default response would be 404 Not Found. When using a web framework, variables in the URL template are usually passed to the corresponding view function as arguments.
Uniform interface is a REST principle which states that all HTTP methods, which are the verbs of the API, should always behave in the same standardized way. In summary:
  • GET - should return a representation of the resource; does not modify anything
  • POST - should create a new instance that belongs to the target collection
  • PUT - should replace the target resource with a new representation (usually only if it exists)
  • DELETE - should delete the target resource
  • PATCH - should describe a change to the resource
In database terminology, unique constraint is a what ensures the uniqueness of each row in a table. Primary key automatically creates a unique constraint, as do unique columns. A unique constraint can also be a combination of columns so that each combination of values between these columns is unique. For example, page numbers by themselves are hardly unique as each book has a first page, but a combination of book and page number is unique - you can only have one first page in a book.
  1. Description
  2. Registering
View functions are Python functions (or methods) that are used for serving HTTP requests. In web applications that often means rendering a view (i.e. a web page). View functions are invoked from URLs by routing. A view function always has application context.
  1. Description
  2. Creation
  3. Activation
A Python virtual environment (virtualenv, venv) is a system for managing packages separately from the operating system's main Python installation. They help project dependency management in multiple ways. First of all, you can install specific versions of packages per project. Second, you can easily get a list of requirements for your project without any extra packages. Third, they can placed in directories owned by non-admin users so that those users can install the packages they need without admin privileges. The venv module which is in charge of creating virtual environments comes with newer versions of Python.
Interface, implemented using web technologies, that exposes a functionality in a remote machine (server). By extension Web API is the exposed functionality itself.