============
Client Usage
============

Connect to a Database
=====================

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

    >>> from crate import client

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

    >>> connection = client.connect(crate_host)

CrateDB 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 = 'http://not_responding_host:4200'
    >>> connection = client.connect([invalid_host, crate_host])

If no ``servers`` are given, the default one ``http://127.0.0.1:4200`` is used::

    >>> connection = client.connect()
    >>> connection.client._active_servers
    ['http://127.0.0.1:4200']

If the option ``error_trace`` is set to ``True``, the client will print a whole
traceback if a server error occurs::

    >>> connection = client.connect([crate_host], error_trace=True)

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)

Authentication
--------------

Users that are trusted as by definition of the ``auth.host_based.config``
setting do not need a password, but only require the ``username`` argument to
connect::

    >>> connection = client.connect([crate_host],
    ...                             username='trusted_me')

To connect to CrateDB with as a user that requires password authentication, you
also need to provide ``password`` as argument for the ``connect()`` call::

    >>> connection = client.connect([crate_host],
    ...                             username='me',
    ...                             password='my_secret_pw')

Default Schema
--------------

To connect to CrateDB and use a different default schema than ``doc``, you can
provide the ``schema`` keyword argument in the ``connect()`` method, like so::

    >>> connection = client.connect([crate_host],
    ...                             schema='custom_schema')

Inserting Data
==============

Use user "crate" for rest of the tests::

    >>> connection = client.connect([crate_host], timeout=2)

Before executing any statement a cursor has to be opened to perform
database operations::

    >>> cursor = connection.cursor()
    >>> cursor.execute("""INSERT INTO locations
    ... (name, date, kind, position) VALUES (?, ?, ?, ?)""",
    ...                ('Einstein Cross', '2007-03-11', 'Quasar', 7))

To bulk insert data you can use the ``executemany`` function::

    >>> cursor.executemany("""INSERT INTO locations
    ... (name, date, kind, position) VALUES (?, ?, ?, ?)""",
    ...                [('Cloverleaf', '2007-03-11', 'Quasar', 7),
    ...                 ('Old Faithful', '2007-03-11', 'Quasar', 7)])
    [{'rowcount': 1}, {'rowcount': 1}]

``executemany`` returns a list of results for every parameter. Each result
contains a rowcount. If an error occurs the rowcount is -2 and the result
may contain an ``error_message`` depending on the error.

Refresh locations:

    >>> cursor.execute("REFRESH TABLE locations")

Selecting Data
==============

To perform the select operation simply execute the statement on the
open 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)
    ['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 order by name")
    >>> result = cursor.fetchmany(2)
    >>> pprint(result)
    [['Aldebaran'], ['Algol']]

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

    >>> cursor.fetchmany()
    [['Allosimanius Syneca']]

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

    >>> cursor.arraysize = 3
    >>> cursor.fetchmany()
    [['Alpha Centauri'], ['Altair'], ['Argabuthon']]

fetchall()
----------

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

    >>> cursor.execute("SELECT name FROM locations order by name")
    >>> result = cursor.fetchall()
    >>> pprint(result)
    [['Aldebaran'],
     ['Algol'],
     ['Allosimanius Syneca'],
     ['Alpha Centauri'],
     ['Altair'],
     ['Argabuthon'],
     ['Arkintoofle Minor'],
     ['Bartledan'],
     ['Cloverleaf'],
     ['Einstein Cross'],
     ['Folfanga'],
     ['Galactic Sector QQ7 Active J Gamma'],
     ['Galaxy'],
     ['North West Ripple'],
     ['Old Faithful'],
     ['Outer Eastern Rim']]

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 order by name")
    >>> result = cursor.fetchone()
    >>> pprint(result)
    ['Aldebaran',
     1373932800000,
     None,
     None,
     None,
     'Star System',
     None,
     1,
     'Max Quordlepleen claims that the only thing left after the end of the '
     'Universe will be the sweets trolley and a fine selection of Aldebaran '
     'liqueurs.',
     None]

    >>> result = cursor.description
    >>> pprint(result)
    (('name', None, None, None, None, None, None),
     ('date', None, None, None, None, None, None),
     ('datetime', None, None, None, None, None, None),
     ('nullable_datetime', None, None, None, None, None, None),
     ('nullable_date', None, None, None, None, None, None),
     ('kind', None, None, None, None, None, None),
     ('flag', None, None, None, None, None, None),
     ('position', None, None, None, None, None, None),
     ('description', None, None, None, None, None, None),
     ('details', 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):
    ...
    crate.client.exceptions.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):
    ...
    crate.client.exceptions.ProgrammingError: Connection closed

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