jake wong jake wong - 3 months ago 14
Python Question

Sqlalchemy if table does not exist

I wrote a module which is to create an empty database file

def create_database():
engine = create_engine("sqlite:///myexample.db", echo=True)
metadata = MetaData(engine)
metadata.create_all()


But in another function, I want to open
myexample.db
database, and create tables to it if it doesn't already have that table.

EG of the first, subsequent table I would create would be:

Table(Variable_TableName, metadata,
Column('Id', Integer, primary_key=True, nullable=False),
Column('Date', Date),
Column('Volume', Float))


(Since it is initially an empty database, it will have no tables in it, but subsequently, I can add more tables to it. Thats what i'm trying to say.)

Any suggestions?

Answer

I've managed to figure out what I intended to do. I used engine.dialect.has_table(engine, Variable_tableName) to check if the database has the table inside. IF it doesn't, then it will proceed to create a table in the database.

Sample code:

engine = create_engine("sqlite:///myexample.db")  # Access the DB Engine
if not engine.dialect.has_table(engine, Variable_tableName):  # If table don't exist, Create.
    metadata = MetaData(engine)
    # Create a table with the appropriate Columns
    Table(Variable_tableName, metadata,
          Column('Id', Integer, primary_key=True, nullable=False), 
          Column('Date', Date), Column('Country', String),
          Column('Brand', String), Column('Price', Float),
    # Implement the creation
    metadata.create_all()

This seems to be giving me what i'm looking for.

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