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Adapter for exposing databases to the web

Project description

webdb provides a simple JSON based database interface for client side data access in web applications.

What is webdb?

webdb is an adapter between you client side application (most probably written in JS in a browser) and your databases on the server. It can be used to access file, SQL, NoSQL and any other database you want using simple HTTP GET and POSTs.

How does it work?

webdb is a cherrypy application that should be mounted under a protected path. Typical would be /database. All the authentication stuff must be handled by cherrypy. The application accesses the database using and instance of webdb.adapters.AbstractDBMS. This instance will dispatch the right database (one might use several databases) and handle the request.

Requests

Requests are HTTP GET requests for pulling and HTTP POST for pushing data. The query is always encoded in JSON objects:

webdbrequest
        .database : string
        .request
                .table : string
                .operation : string
                .parameters: object
webdbrequest.database
String name of the database. This name will be used to dispatch the right database adapter.
webdbrequest.request.table
String name of the table to access.
webdbrequest.request.operation
String name of the operation. It is one of INSERT, UPDATE, DELETE, SELECT
webdbrequest.request.parameters

Is a JSON object containing the parameters of the query. The structure depends on the operation:

INSERT

The parameter is just a map of key value pairs that will be attempted to put:

.parameters: {string: value}
UPDATE

The parameter is an object containing a set and a where block:

.parameters
        .where: {string: value}
        .set: {string: value}

All key value pairs in where will be interpreted as AND joined conditions, all key value pairs in set will be interpreted as substitutions for the current values.

DELETE

The parameter is a map {string: value} that will be interpreted as AND joined conditions:

.parameters: {string: value}
SELECT

The parameter is an object containing a where and a what block:

.parameters
        .where: {string: value}
        .what: list

where will be interpreted as in UPDATE, what is the list of columns to fetch.

value is one of the following types: string, integer, float, boolean, date, time, datetime.

See Handling Date and Time.

The server will return data depending on what the adapter returns. If the adapter returns an exception, the server will set the HTTP status to 404, the content-type to text/plain and return a (maybe) useful text. If the server returns a structured result (for instance the result of a SQL SELECT) it will set the HTTP status to 200 and the content-type to application/json and return the json encoded data. If the server returns nothing but the query did succeed it will set the HTTP status to 204 and return nothing.

Isolating Users

There might be several users accessing the same database/table/whatever. To isolate access to this shared data the inject operation can be used. The AbstractDBMS has an attribute inject that should be a nested function returning the attribute value to inject and an attribute inject_as that should be set to the name of the table column that should be inserted.

A typical application might set the username in the session and inject the username in the query:

dbms = AbstractDBMS(
                inject = lambda: cherrypy.session["username"],
                inject_as = "username")

Note: This will not actually work. One cannot instantiate AbstractDBMS, as it is abstract. This sample is just meant to be a hint how one can implement injections.

Handling Date and Time

Date and time are handled as JSON objects with a magic attribute (the __type__)

time
        .__type__ = "time"
        .hour: int
        .minute: int
        .second: int
        .microsecond: int
        .utcoffset: int

date
        .__type__ = "date"
        .year: int
        .month: int
        .day: int

datetime
        .__type__ = "datetime"
        .year: int
        .month: int
        .day: int
        .hour: int
        .minute: int
        .second: int
        .microsecond: int
        .utcoffset: int

See also:

One can omit some attributes, they will be filled with zeros automatically.

Files

webdb is also capable of serving files. This can be done by creating a webdb.interface.file.FileInterface instance and providing it with a webdb.files.dispatcher.AbstractFileDispatcher.

There are already three implementations:

UserFileDispatcher
Allows full access to a private directory for all users.
QuotaUserFileDispatcher
Allows full access to a private directory for all users. Rejects to write once the quota is exceeded.
SQLFileDispatcher
Allows access to files according to a database.

Project details


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