On Fri, Jul 17, 2020, at 7:20 AM, Bob Fang wrote:
> Hi I have seen two/three ways to declare index on table:
>
> 1. use index=True
>
> class Model(Base):
> __tablename__ = "model"
> id = sa.Column(sa.Integer, primary_key=True)
> field_1 = sa.Column(sa.Integer, index=True)
>
> 2. use __table_args__:
>
> class Model(Base):
> __tablename__ = "model"
> id = sa.Column(sa.Integer)
> field_1 = sa.Column(sa.Integer)
>
> __table_args__ = (sa.Index("field_1_index", "field_1"))
>
> 3. use Index statement:
>
> class Model(Base):
> __tablename__ = "model"
> id = sa.Column(sa.Integer)
> field_1 = sa.Column(sa.Integer)
>
> Index("field_1_index", "field1")
>
> My question is what's the difference between these 3? Also if I have mixed
> two of them, what will happen? By this I mean consider the following example;
There's no difference between using __table_args__ and the separate Index
field, except when you use the separate Index field, you need to put a real
Column that's associated with your Table in there, and not a string name,
otherwise it will not be able to associate itself with the Table.
the "index=True" is shorthand for Index(None, column), where "None" is the
name. the name is generated from the default naming convention for the
metadata which defaults for the index to "ix_tablename_colname".
>
> class Model(Base):
> __tablename__ = "model"
> id = sa.Column(sa.Integer, *primary_key=True*)
> field_1 = sa.Column(sa.Integer)
>
> __table_args__ = (*sa.Index("field_1_index", "field_1")*)
>
> Here we are mixing method 1 and 2. From my experiment it seems Postgres can
> accept this without any problem but Sqlite rejects it outright. Why this
> happens?
>
> Thanks!
> Bob
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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