Get existing table using SQLAlchemy MetaData

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I have a table that already exists:

USERS_TABLE = Table("users", META_DATA,
                    Column("id", Integer, Sequence("user_id_seq"), primary_key=True),
                    Column("first_name", String(255)),
                    Column("last_name", String(255))
                   )

I created this table by running this:

CONN = create_engine(DB_URL, client_encoding="UTF-8")
META_DATA = MetaData(bind=CONN, reflect=True)
# ... table code
META_DATA.create_all(CONN, checkfirst=True)

the first time it worked and I was able to create the table. However, the 2nd time around I got this error:

sqlalchemy.exc.InvalidRequestError: Table 'users' is already defined for this MetaData instance.  Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

which makes sense since the table users already exists. I'm able to see if the table exists like so:

TABLE_EXISTS = CONN.dialect.has_table(CONN, "users")

However, how do I actually get the existing table object? I can't find this anywhere in the documentation. Please help.

Reflecting Database Objects — SQLAlchemy 1.3 Documentation, The Table constructor actually returns to you the already-existing The MetaData object can also get a listing of tables and reflect the full set. Table.extend_existing will also work in conjunction with Table.autoload to run a new reflection operation against the database, even if a Table of the same name is already present in the target MetaData; newly reflected Column objects and other options will be added into the state of the Table, potentially overwriting existing columns and

__table_args__ = {'extend_existing': True}

right below __tablename__

Describing Databases with MetaData — SQLAlchemy 1.3 , To add a constraint to an existing relational database table, from sqlalchemy. sql import table, column, select t = table('t',� method sqlalchemy.engine.reflection.Inspector. get_table_options (table_name, schema = None, ** kw) ¶ Return a dictionary of options specified when the table of the given name was created. This currently includes some options that apply to MySQL tables. Parameters. table_name¶ – string name of the table. For special quoting, use quoted_name.

I tried using the checkfirst=True alone but found I also had to add the extend_existing before it stopped giving me the sqlalchemy.exc.InvalidRequestError:

        metaData = MetaData(bind=engine, reflect=True)  

        with engine.connect() as connection:

            for dataItem in dataItemList:
                metaData.reflect()
                db.Table('roles_users',
                db.Column('user_id', db.Integer(), db.ForeignKey('user.id')),
                db.Column('role_id', db.Integer(), db.ForeignKey('role.id')),
                Column("data_value", String(255)),
                extend_existing=True)
                metaData.create_all(connection, checkfirst=True)  

Using SQLAlchemy to navigate an existing database, SQLAlchemy reflection. Reflection uses metadata property to access schema constructs. It offers a few methods to access table objects, which do� SQLAlchemy Column object represents a column in a database table which is in turn represented by a Tableobject. Metadata contains definitions of tables and associated objects such as index, view, triggers, etc. Hence an object of MetaData class from SQLAlchemy Metadata is a collection of Table objects and their associated schema constructs.

SQLAlchemy — pysheeet, from sqlalchemy import create_engine from sqlalchemy import MetaData from inspect(engine) # Get table information print(inspector.get_table_names())� Viewing Table Details. SQLAlchemy can be used to automatically load tables from a database using something called reflection. Reflection is the process of reading the database and building the metadata based on that information. example

Normally, the Column objects used here are expected to be part of the target Table that is the table to be updated. However when using MySQL, a multiple-table UPDATE statement can refer to columns from any of the tables referred to in the WHERE clause. The values referred to in values are typically: a literal data value (i.e. string, number, etc.)

I get the output <class 'sqlalchemy.sql.base.ImmutableColumnCollection'> printed once for each column in the table. Furthermore, print columns prints ['users.column_name_1', 'users.column_name_2', 'users.column_name_3'.] Is it possible to get the column names without the table name being included?

Comments
  • Where is the sqlite:///db.sql file actually saved? I cannot locate this file anywhere after creation...
  • @SeanPianka: it should be at the directory where your script is executed
  • Can you please provide an example? What do you mean by "below"?