Hi Simon,
The tables and sample data are below.
So first I search the nodes table for a and b, getting the node_id of them
(in this example, 1 and 2).
Then using the SQL statement, I would get all posts that have 1 and 2 as
the node_id. So in the example data, 100, 103, 108 will be returned as
these posts contain the nodes 1 and 2.
Hope this helps.
Desmond
-------------
CREATE SEQUENCE IF NOT EXISTS nodes_id_seq;
CREATE TABLE "public"."nodes" (
"id" int8 NOT NULL DEFAULT nextval('nodes_id_seq'::regclass),
"project_uuid" uuid NOT NULL,
"topic" varchar(20) NOT NULL,
PRIMARY KEY ("id")
);
CREATE SEQUENCE IF NOT EXISTS posts_id_seq;
CREATE TABLE "public"."posts" (
"id" int8 NOT NULL DEFAULT nextval('posts_id_seq'::regclass),
"project_uuid" uuid NOT NULL,
PRIMARY KEY ("id")
);
CREATE TABLE "public"."pn" (
"post_id" int8 NOT NULL,
"node_id" int8 NOT NULL,
PRIMARY KEY ("post_id","node_id")
);
INSERT INTO "public"."nodes" ("id", "project_uuid", "topic", "size",
"given_id") VALUES
('1', '42a8e275-f153-452b-99d3-645bdd513ca9', 'a'),
('2', '42a8e275-f153-452b-99d3-645bdd513ca9', 'b'),
('3', '42a8e275-f153-452b-99d3-645bdd513ca9', 'c'),
('4', '42a8e275-f153-452b-99d3-645bdd513ca9', 'd')
INSERT INTO "public"."posts" ("id", "project_uuid") VALUES
('100', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('101', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('102', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('103', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('104', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('105', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('106', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('107', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('108', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('109', '42a8e275-f153-452b-99d3-645bdd513ca9'),
('110', '42a8e275-f153-452b-99d3-645bdd513ca9')
INSERT INTO "public"."pn" ("post_id", "node_id") VALUES
('1', '100'),
('2', '100'),
('3', '100'),
('2', '101'),
('3', '101'),
('4', '101'),
('5', '101'),
('3', '102'),
('4', '102'),
('1', '103'),
('2', '103'),
('3', '103'),
('2', '104'),
('4', '104'),
('1', '105'),
('4', '105'),
('3', '105'),
('3', '106'),
('4', '106'),
('4', '107'),
('1', '108'),
('2', '108'),
('3', '109'),
('1', '109'),
('4', '109'),
('2', '110'),
('3', '110')
ALTER TABLE "public"."posts" ADD FOREIGN KEY ("project_uuid") REFERENCES
"public"."projects"("uuid");
ALTER TABLE "public"."pn" ADD FOREIGN KEY ("post_id") REFERENCES
"public"."posts"("id");
ALTER TABLE "public"."pn" ADD FOREIGN KEY ("node_id") REFERENCES
"public"."nodes"("id");
On Mon, 10 Jun 2019 at 17:08, Simon King <si...@simonking.org.uk> wrote:
> Hi Desmond.
>
> I don't really understand your table structure. Could you present it
> in the form of a standalone script that we can run (including sample
> data)?
>
> Thanks,
>
> Simon
>
> On Mon, Jun 10, 2019 at 2:57 AM Desmond Lim <limwen...@gmail.com> wrote:
> >
> > Hi there,
> >
> > I really have no idea how to do this via sqlalchemy. I have 2 tables:
> >
> > class NodesModel(db.Model):
> > __tablename__ = 'nodes'
> >
> > id = db.Column(db.BigInteger, primary_key=True)
> > topic = db.Column(db.String(20), nullable=False)
> >
> > pn = relationship("PNModel", backref="nodes")
> >
> > class PNModel(db.Model):
> > __tablename__ = 'pn'
> >
> > post_id = db.Column(db.BigInteger, db.ForeignKey('posts.id'),
> primary_key=True)
> > node_id = db.Column(db.BigInteger, db.ForeignKey('nodes.id'),
> primary_key=True)
> >
> >
> > I will get a list of nodes that have the topic (e.g. one, two). Then
> taking the nodes, I'll select the PN that have both nodes (it can be 1 or
> more) associated with it.
> >
> > e.g.
> >
> >
> >
> > I'm doing it this way at this point:
> >
> > nodes = NodesModel.find_by_topic_list(topic_list)
> > node_id_list = [node.id for node in nodes]
> >
> > Then running this sql statement:
> > WITH pn_1 AS (SELECT post_id, ARRAY_AGG(DISTINCT node_id) AS nodes
> > FROM pn GROUP BY post_id),
> > nodes_1 AS (SELECT ARRAY_AGG(DISTINCT id) AS s_nodes
> > FROM pn WHERE node_id IN (dict(node_id_list))
> > SELECT DISTINCT post_id FROM pn_1
> > WHERE nodes_1 = (SELECT s_nodes FROM select_nodes);
> >
> > There has to be a better and more elegant way to do this with SQLAlchemy
> and I can't seem to figure it out. I've tried using subqueries and then I
> realised that I'm actually calling the nodes table twice, which I shouldn't
> have to.
> >
> > Can anyone tell me how to use the nodes table to get the post_id form pn
> (after which getting the post should be easy via ORM should be easy, I
> think).
> >
> > Thanks.
> > Desmond
> >
> > --
> > 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
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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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