i'm working on a postgresql database and i have an issue :
i want to create a table applicant with a column categories_ids (that mean that an applicant can have multiple categories) and i want create a foreign key constraint between this column and the column id of categories table. But pgadmin says that is impossible :
foreign key constraint "fk_categories_ids" cannot be implemented
DÉTAIL : Key columns "categories_ids" and "id" are of incompatible types: integer[] and integer.
EDIT 1 :
CREATE TABLE public.applicants
(
-- Hérité(e) from table users: id integer NOT NULL DEFAULT nextval('users_id_seq'::regclass),
-- Hérité(e) from table users: email character(60) NOT NULL,
-- Hérité(e) from table users: "firstName" character(50) NOT NULL,
-- Hérité(e) from table users: "lastName" character(50) NOT NULL,
-- Hérité(e) from table users: password character(50) NOT NULL,
-- Hérité(e) from table users: role_id integer NOT NULL DEFAULT nextval('users_role_id_seq'::regclass),
home boolean NOT NULL,
"fullTime" boolean,
"partTime" boolean NOT NULL,
freelance boolean NOT NULL,
internship boolean NOT NULL,
"minSalary" integer,
domain_id integer,
categories_ids integer[],
skills_ids integer[],
locations_ids integer[],
"jobExperiences_ids" integer[],
CONSTRAINT pk_applicant_id PRIMARY KEY (id),
CONSTRAINT fk_domain_id FOREIGN KEY (domain_id)
REFERENCES public.domains (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
INHERITS (public.users)
WITH (
OIDS=FALSE
);
Delete the categories_ids integer[]
field and:
create table applicant_category (
applicant_id int references applicants(id),
category_id int references category(category_id),
primary key (applicant_id, category_id)
)
You cannot create FK on array column. Not supported. So either use EAV model ( https://en.wikipedia.org/wiki/Entity%E2%80%93attribute%E2%80%93value_model , so 3 tables instead of 2), or work without Foreign Keys (you can create custom triggers to emulate them, though).
There are some articles comparing EAV with using "non-primitive" ( int[]
, hstore
, jsonb
) data types -- for example http://coussej.github.io/2016/01/14/Replacing-EAV-with-JSONB-in-PostgreSQL/ and https://wiki.hsr.ch/Datenbanken/files/Benchmark_of_KVP_vs. hstore -_doc.pdf have some benchmarks.
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