"paginate" is not an SQLAlchemy function, so you'd be better off
asking the author of whatever is providing that feature.
However, I would guess that maybe paginate is naively applying
something like "LIMIT 20" to the query. This doesn't work properly
when you join along a one-to-many relationship, because if you have
(for example) 2 "parent" objects, each with 5 "child" objects, the
query will return 10 rows, but SQLAlchemy de-duplicates the results to
return just the 2 parent objects.
Simon
On Thu, Aug 13, 2020 at 3:31 PM Prerna Pandit <prerna.m.pan...@gmail.com> wrote:
>
> Hello, I've been struggling with this issue for the past couple of days and
> would really, truly appreciate if someone could please give me pointers or
> direction as to what I might be missing.
>
>
> Here are my models;
> class Aggregate(db.Model):
> id = db.Column(UUID(as_uuid=True), primary_key=True,
> server_default=db.text('uuid_generate_v4()'))
> blocks = db.relationship('AggregateBlock', cascade='all, delete-orphan',
> passive_deletes=True,
> back_populates='aggregate')..
>
>
> class AggregateBlock(db.Model):
>
> id = db.Column(UUID(as_uuid=True), primary_key=True,
> server_default=db.text('uuid_generate_v4()'))
> block_id = db.Column(UUID(as_uuid=True),
> db.ForeignKey('blocks.id', ondelete='CASCADE'),
> nullable=False, index=True)
> aggregate_id = db.Column(UUID(as_uuid=True),
> db.ForeignKey('aggregates.id',
> ondelete='RESTRICT'), nullable=False)
> block = db.relationship('Block', back_populates='aggregates')
> aggregate = db.relationship('Aggregate', back_populates='blocks')
>
>
>
>
> class Block(db.Model):
> id = db.Column(UUID(as_uuid=True), primary_key=True,
> server_default=db.text('uuid_generate_v4()'))
> is_complete = db.Column(db.Boolean, default=False)
> aggregates = db.relationship('AggregateBlock', cascade='all,
> delete-orphan',
> passive_deletes=True, back_populates='block')
>
>
> from flask_sqlalchemy import SQLAlchemy
> db = SQLAlchemy()
>
> select =
> db.session.query(Aggregate).join(AggregateBlock).join(Block).filter(Block.is_complete
> == complete)
>
> print(len(select.all())
>
> print(len(select.paginate(per_page=20).items())
>
>
> If I do a select.all(), I get the right number of rows which is 47. However,
> if I try to paginate for a per_page size say 20, I lot a less rows like 11.
> select.paginate(per_page=20).
> The number could go up to 21 or so as I increase the page size. Why would
> paginate decrease the number of returned records?
>
> --
> 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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--
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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