Adding upstream version 3.1.7.upstream/3.1.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 151 insertions, 0 deletions

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+`sql` -- SQL string composition
+===============================
+
+.. index::
+    double: Binding; Client-Side
+
+.. module:: psycopg.sql
+
+The module contains objects and functions useful to generate SQL dynamically,
+in a convenient and safe way. SQL identifiers (e.g. names of tables and
+fields) cannot be passed to the `~psycopg.Cursor.execute()` method like query
+arguments::
+
+    # This will not work
+    table_name = 'my_table'
+    cur.execute("INSERT INTO %s VALUES (%s, %s)", [table_name, 10, 20])
+
+The SQL query should be composed before the arguments are merged, for
+instance::
+
+    # This works, but it is not optimal
+    table_name = 'my_table'
+    cur.execute(
+        "INSERT INTO %s VALUES (%%s, %%s)" % table_name,
+        [10, 20])
+
+This sort of works, but it is an accident waiting to happen: the table name
+may be an invalid SQL literal and need quoting; even more serious is the
+security problem in case the table name comes from an untrusted source. The
+name should be escaped using `~psycopg.pq.Escaping.escape_identifier()`::
+
+    from psycopg.pq import Escaping
+
+    # This works, but it is not optimal
+    table_name = 'my_table'
+    cur.execute(
+        "INSERT INTO %s VALUES (%%s, %%s)" % Escaping.escape_identifier(table_name),
+        [10, 20])
+
+This is now safe, but it somewhat ad-hoc. In case, for some reason, it is
+necessary to include a value in the query string (as opposite as in a value)
+the merging rule is still different. It is also still relatively dangerous: if
+`!escape_identifier()` is forgotten somewhere, the program will usually work,
+but will eventually crash in the presence of a table or field name with
+containing characters to escape, or will present a potentially exploitable
+weakness.
+
+The objects exposed by the `!psycopg.sql` module allow generating SQL
+statements on the fly, separating clearly the variable parts of the statement
+from the query parameters::
+
+    from psycopg import sql
+
+    cur.execute(
+        sql.SQL("INSERT INTO {} VALUES (%s, %s)")
+            .format(sql.Identifier('my_table')),
+        [10, 20])
+
+
+Module usage
+------------
+
+Usually you should express the template of your query as an `SQL` instance
+with ``{}``\-style placeholders and use `~SQL.format()` to merge the variable
+parts into them, all of which must be `Composable` subclasses. You can still
+have ``%s``\-style placeholders in your query and pass values to
+`~psycopg.Cursor.execute()`: such value placeholders will be untouched by
+`!format()`::
+
+    query = sql.SQL("SELECT {field} FROM {table} WHERE {pkey} = %s").format(
+        field=sql.Identifier('my_name'),
+        table=sql.Identifier('some_table'),
+        pkey=sql.Identifier('id'))
+
+The resulting object is meant to be passed directly to cursor methods such as
+`~psycopg.Cursor.execute()`, `~psycopg.Cursor.executemany()`,
+`~psycopg.Cursor.copy()`, but can also be used to compose a query as a Python
+string, using the `~Composable.as_string()` method::
+
+    cur.execute(query, (42,))
+    full_query = query.as_string(cur)
+
+If part of your query is a variable sequence of arguments, such as a
+comma-separated list of field names, you can use the `SQL.join()` method to
+pass them to the query::
+
+    query = sql.SQL("SELECT {fields} FROM {table}").format(
+        fields=sql.SQL(',').join([
+            sql.Identifier('field1'),
+            sql.Identifier('field2'),
+            sql.Identifier('field3'),
+        ]),
+        table=sql.Identifier('some_table'))
+
+
+`!sql` objects
+--------------
+
+The `!sql` objects are in the following inheritance hierarchy:
+
+|   `Composable`: the base class exposing the common interface
+|   ``|__`` `SQL`: a literal snippet of an SQL query
+|   ``|__`` `Identifier`: a PostgreSQL identifier or dot-separated sequence of identifiers
+|   ``|__`` `Literal`: a value hardcoded into a query
+|   ``|__`` `Placeholder`: a `%s`\ -style placeholder whose value will be added later e.g. by `~psycopg.Cursor.execute()`
+|   ``|__`` `Composed`: a sequence of `!Composable` instances.
+
+
+.. autoclass:: Composable()
+
+    .. automethod:: as_bytes
+    .. automethod:: as_string
+
+
+.. autoclass:: SQL
+
+    .. versionchanged:: 3.1
+
+        The input object should be a `~typing.LiteralString`. See :pep:`675`
+        for details.
+
+    .. automethod:: format
+
+    .. automethod:: join
+
+
+.. autoclass:: Identifier
+
+.. autoclass:: Literal
+
+    .. versionchanged:: 3.1
+        Add a type cast to the representation if useful in ambiguous context
+        (e.g. ``'2000-01-01'::date``)
+
+.. autoclass:: Placeholder
+
+.. autoclass:: Composed
+
+    .. automethod:: join
+
+
+Utility functions
+-----------------
+
+.. autofunction:: quote
+
+.. data::
+    NULL
+    DEFAULT
+
+    `sql.SQL` objects often useful in queries.