# Crate Client Usage

## Connect to a Database

Before we can start we have to import the crate client:

    >>> from crate import client

The client provides a `connect()` function which is used to establish a connection, the first argument is the server to connect to:

    >>> connection = client.connect(crate_host)

Crate is a clustered database providing high availability through replication. In order for clients to make use of this property it is recommended to specify all hosts of the cluster. This way if a server does not respond, the request is automatically routed to the next server:

    >>> invalid_host = 'not_responding_host:9200'
    >>> connection = client.connect([invalid_host, crate_host])

If no `servers` are given, the default one `127.0.0.1:9200` is used:

    >>> connection = client.connect()
    >>> connection.client._active_servers
    ['127.0.0.1:9200']

It’s possible to define a default timeout value in seconds for all servers using the optional parameter `timeout`:

    >>> connection = client.connect([crate_host, invalid_host], timeout=5)

## Selecting Some Data

To execute a command a cursor has to be opened to perform database operations:

    >>> cursor = connection.cursor()
    >>> cursor.execute("SELECT name FROM locations where name = ?", ('Algol',))

To retrieve a row we can use one of the cursor’s fetch functions (described below).

### fetchone()

`fetchone()` with each call returns the next row from the results:

    >>> result = cursor.fetchone()
    >>> pprint(result)
    [u'Algol']

If no more data is available, an empty result is returned:

    >>> while cursor.fetchone():
    ...     pass
    >>> cursor.fetchone()

### fetchmany()

`fetch_many()` returns a list of all remaining rows, containing no more than the specified size of rows:

    >>> cursor.execute("SELECT name FROM locations")
    >>> result = cursor.fetchmany(2)
    >>> pprint(result)
    [[u'Algol'], [u'Folfanga']]

If a size is not given, the cursor’s arraysize, which defaults to ‘1’, determines the number of rows to be fetched:

    >>> cursor.fetchmany()
    [[u'Aldebaran']]

It’s also possible to change the cursors arraysize to an other value:

    >>> cursor.arraysize = 3
    >>> cursor.fetchmany()
    [[u'Argabuthon'], [u'Bartledan'], [u'Galactic Sector QQ7 Active J Gamma']]

### fetchall()

`fetchall()` returns a list of all remaining rows:

    >>> cursor.execute("SELECT name FROM locations")
    >>> result = cursor.fetchall()
    >>> pprint(result)
    [[u'Algol'],
     [u'Folfanga'],
     [u'Aldebaran'],
     [u'Argabuthon'],
     [u'Bartledan'],
     [u'Galactic Sector QQ7 Active J Gamma'],
     [u'Allosimanius Syneca'],
     [u'Arkintoofle Minor'],
     [u'Outer Eastern Rim'],
     [u'Altair']]

## Cursor Description

The `description` property of the cursor returns a sequence of 7-item sequences containing the column name as first parameter. Just the name field is supported, all other fields are ‘None’:

    >>> cursor.execute("SELECT * FROM locations")
    >>> result = cursor.fetchone()
    >>> pprint(result)
    [u'2013-07-16T00:00:00.000Z',
     None,
     u'Algol is the home of the Algolian Suntiger, ...',
     u'Star System',
     u'Algol',
     2]

    >>> result = cursor.description
    >>> pprint(result)
    ((u'date', None, None, None, None, None, None),
     (u'datetime', None, None, None, None, None, None),
     (u'description', None, None, None, None, None, None),
     (u'kind', None, None, None, None, None, None),
     (u'name', None, None, None, None, None, None),
     (u'position', None, None, None, None, None, None))

## Closing the Cursor

The following command closes the cursor:

    >>> cursor.close()

If a cursor is closed, it will be unusable from this point forward. If any operation is attempted to a closed cursor an `ProgrammingError` will be raised.

    >>> cursor.execute("SELECT * FROM locations")
    Traceback (most recent call last):
    ...
    ProgrammingError: Cursor closed

## Closing the Connection

The following command closes the connection:

    >>> connection.close()

If a connection is closed, it will be unusable from this point forward. If any operation using the connection is attempted to a closed connection an `ProgrammingError` will be raised:

    >>> cursor.execute("SELECT * FROM locations")
    Traceback (most recent call last):
    ...
    ProgrammingError: Connection closed

    >>> cursor = connection.cursor()
    Traceback (most recent call last):
    ...
    ProgrammingError: Connection closed