Blocking API

Connection

function

connect()

connect(dsn=None, *, host=None, port=None, admin=None, user=None, password=None, database=None, timeout=60)

Establish a connection to an EdgeDB server.

Parameters

dsn – If this parameter does not start with edgedb:// then this is a name of an instance.Otherwise it specifies a single string in the connection URI format: edgedb://user:password@host:port/database?option=value. The following options are recognized: host, port, user, database, password.
host – Database host address as one of the following:
- an IP address or a domain name;
- an absolute path to the directory containing the database server Unix-domain socket (not supported on Windows);
- a sequence of any of the above, in which case the addresses will be tried in order, and the first successful connection will be returned.
If not specified, the following will be tried, in order:
- host address(es) parsed from the dsn argument,
- the value of the EDGEDB_HOST environment variable,
- on Unix, common directories used for EdgeDB Unix-domain sockets: "/run/edgedb" and "/var/run/edgedb",
- "localhost".
port – Port number to connect to at the server host (or Unix-domain socket file extension). If multiple host addresses were specified, this parameter may specify a sequence of port numbers of the same length as the host sequence, or it may specify a single port number to be used for all host addresses.If not specified, the value parsed from the dsn argument is used, or the value of the EDGEB_PORT environment variable, or 5656 if neither is specified.
admin – If True, try to connect to the special administration socket.
user – The name of the database role used for authentication.If not specified, the value parsed from the dsn argument is used, or the value of the EDGEDB_USER environment variable, or the operating system name of the user running the application.
database – The name of the database to connect to.If not specified, the value parsed from the dsn argument is used, or the value of the EDGEDB_DATABASE environment variable, or the operating system name of the user running the application.
password – Password to be used for authentication, if the server requires one. If not specified, the value parsed from the dsn argument is used, or the value of the EDGEDB_PASSWORD environment variable. Note that the use of the environment variable is discouraged as other users and applications may be able to read it without needing specific privileges.
timeout (float) – Connection timeout in seconds.

Returns

A BlockingIOConnection instance.

The connection parameters may be specified either as a connection URI in dsn, or as specific keyword arguments, or both. If both dsn and keyword arguments are specified, the latter override the corresponding values parsed from the connection URI.

Returns a new BlockingIOConnection object.

Example:

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>>>

import edgedb

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>>>

con = edgedb.connect(user='edgedeb')

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>>>

con.query_one('SELECT 1 + 1')

{2}

class

BlockingIOConnection

A representation of a database session.

Connections are created by calling connect().

method

BlockingIOConnection.query()

BlockingIOConnection.query(query, *args, **kwargs)

Run a query and return the results as a edgedb.Set instance.

Parameters

query (str) – Query text.
args – Positional query arguments.
kwargs – Named query arguments.

Returns

An instance of edgedb.Set containing the query result.

Note that positional and named query arguments cannot be mixed.

method

BlockingIOConnection.query_one()

BlockingIOConnection.query_one(query, *args, **kwargs)

Run a singleton-returning query and return its element.

Parameters

query (str) – Query text.
args – Positional query arguments.
kwargs – Named query arguments.

Returns

Query result.

The query must return exactly one element. If the query returns more than one element, an edgedb.ResultCardinalityMismatchError is raised, if it returns an empty set, an edgedb.NoDataError is raised.

Note, that positional and named query arguments cannot be mixed.

method

BlockingIOConnection.query_json()

BlockingIOConnection.query_json(query, *args, **kwargs)

Run a query and return the results as JSON.

Parameters

query (str) – Query text.
args – Positional query arguments.
kwargs – Named query arguments.

Returns

A JSON string containing an array of query results.

Note, that positional and named query arguments cannot be mixed.

Caution is advised when reading decimal values using this method. The JSON specification does not have a limit on significant digits, so a decimal number can be losslessly represented in JSON. However, the default JSON decoder in Python will read all such numbers as float values, which may result in errors or precision loss. If such loss is unacceptable, then consider casting the value into str and decoding it on the client side into a more appropriate type, such as Decimal.

method

BlockingIOConnection.query_one_json()

BlockingIOConnection.query_one_json(query, *args, **kwargs)

Run a singleton-returning query and return its element in JSON.

Parameters

query (str) – Query text.
args – Positional query arguments.
kwargs – Named query arguments.

Returns

Query result encoded in JSON.

Note, that positional and named query arguments cannot be mixed.

method

BlockingIOConnection.execute()

BlockingIOConnection.execute(query)

Execute an EdgeQL command (or commands).

Parameters

query (str) – Query text.

The commands must take no arguments.

Example:

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>>> 
... 
... 
... 
... 
... 
...

con.execute('''
    CREATE TYPE MyType {
        CREATE PROPERTY a -> int64
    };
    FOR x IN {100, 200, 300}
    UNION INSERT MyType { a := x };
''')

If the results of query are desired, query() or query_one() should be used instead.

method

BlockingIOConnection.retrying_transaction()

Open a retryable transaction loop.

This is the preferred method of initiating and running a database transaction in a robust fashion. The retrying_transaction() transaction loop will attempt to re-execute the transaction loop body if a transient error occurs, such as a network error or a transaction serialization error.

Returns an instance of Retry.

See Transactions for more details.

Example:

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for tx in con.retrying_transaction():
    with tx:
        value = tx.query_one("SELECT Counter.value")
        tx.execute(
            "UPDATE Counter SET { value := <int64>$value }",
            value=value + 1,
        )

Note that we are executing queries on the tx object rather than on the original connection.

method

BlockingIOConnection.raw_transaction()

Execute a non-retryable transaction.

Contrary to retrying_transaction(), raw_transaction() will not attempt to re-run the nested code block in case a retryable error happens.

This is a low-level API and it is advised to use the retrying_transaction() method instead.

A call to raw_transaction() returns AsyncIOTransaction.

Example:

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with con.raw_transaction() as tx:
    value = tx.query_one("SELECT Counter.value")
    tx.execute(
        "UPDATE Counter SET { value := <int64>$value }",
        value=value + 1,
    )

Note that we are executing queries on the tx object, rather than on the original connection con.

method

BlockingIOConnection.transaction()

BlockingIOConnection.transaction(isolation=None, readonly=None, deferrable=None)

Deprecated. Use retrying_transaction() or raw_transaction().

Create a Transaction object.

Parameters

isolation – Transaction isolation mode, can be one of: 'serializable', 'repeatable_read'. If not specified, the server-side default is used.
readonly – Specifies whether or not this transaction is read-only. If not specified, the server-side default is used.
deferrable – Specifies whether or not this transaction is deferrable. If not specified, the server-side default is used.

method

BlockingIOConnection.close()

Close the connection gracefully.

method

BlockingIOConnection.is_closed()

Return True if the connection is closed.

Transactions

The most robust way to execute transactional code is to use the retrying_transaction() loop API:

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for tx in pool.retrying_transaction():
    with tx:
        tx.execute("INSERT User { name := 'Don' }")

Note that we execute queries on the tx object in the above example, rather than on the original connection pool pool object.

The retrying_transaction() API guarantees that:

Transactions are executed atomically;
If a transaction is failed for any of the number of transient errors (i.e. a network failure or a concurrent update error), the transaction would be retried;
If any other, non-retryable exception occurs, the transaction is rolled back, and the exception is propagated, immediately aborting the retrying_transaction() block.

The key implication of retrying transactions is that the entire nested code block can be re-run, including any non-querying Python code. Here is an example:

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for tx in pool.retrying_transaction():
    with tx:
        user = tx.query_one(
            "SELECT User { email } FILTER .login = <str>$login",
            login=login,
        )
        data = httpclient.get(
            'https://service.local/email_info',
            params=dict(email=user.email),
        )
        user = tx.query_one('''
                UPDATE User FILTER .login = <str>$login
                SET { email_info := <json>$data}
            ''',
            login=login,
            data=data,
        )

In the above example, the execution of the HTTP request would be retried too. The core of the issue is that whenever transaction is interrupted user might have the email changed (as the result of concurrent transaction), so we have to redo all the work done.

Generally it’s recommended to not execute any long running code within the transaction unless absolutely necessary.

Transactions allocate expensive server resources and having too many concurrently running long-running transactions will negatively impact the performance of the DB server.