SQL insert while checking that one of keys is equal to a field in another table - sql

Question

I'm using sequelize and postgresql but I think this is a more generic SQL/table question.
I have a setup similar to:
CREATE TABLE "Mixtime" (
id bigint NOT NULL,
duration character varying(255) NOT NULL,
created_at timestamp with time zone NOT NULL,
updated_at timestamp with time zone NOT NULL,
spell_id bigint NOT NULL,
ingredient_id bigint NOT NULL,
user_id bigint NOT NULL
);
CREATE TABLE "Spell" (
id bigint NOT NULL,
instructions character varying(5000) NOT NULL,
created_at timestamp with time zone NOT NULL,
user_id bigint NOT NULL
);
CREATE TABLE "Ingredient" (
id bigint NOT NULL,
ing_name character varying(255) NOT NULL,
created_at timestamp with time zone NOT NULL,
updated_at timestamp with time zone NOT NULL,
user_id bigint NOT NULL
);
CREATE TABLE "Users" (
id bigint NOT NULL,
user_name character varying(255) NOT NULL,
created_at timestamp with time zone NOT NULL,
updated_at timestamp with time zone NOT NULL,
);
ALTER TABLE ONLY "Mixtime"
ADD CONSTRAINT "Mixtime_pkey" PRIMARY KEY (id);
ALTER TABLE ONLY "Spell"
ADD CONSTRAINT "Spell_pkey" PRIMARY KEY (id);
ALTER TABLE ONLY "Ingredient"
ADD CONSTRAINT "Ingredient_pkey" PRIMARY KEY (id);
ALTER TABLE ONLY "Users"
ADD CONSTRAINT "Users_pkey" PRIMARY KEY (id);
ALTER TABLE ONLY "Mixtime"
ADD CONSTRAINT "Mixtime_spell_id_fkey" FOREIGN KEY (spell_id) REFERENCES "Spell"(id) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY "Mixtime"
ADD CONSTRAINT "Mixtime_ingredient_id_fkey" FOREIGN KEY (ingredient_id) REFERENCES "Ingredient"(id) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY "Mixtime"
ADD CONSTRAINT "Mixtime_user_id_fkey" FOREIGN KEY (user_id) REFERENCES "Users"(id) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY "Spell"
ADD CONSTRAINT "Spell_user_id_fkey" FOREIGN KEY (user_id) REFERENCES "Users"(id) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY "Ingredient"
ADD CONSTRAINT "Ingredient_user_id_fkey" FOREIGN KEY (user_id) REFERENCES "Users"(id) ON UPDATE CASCADE ON DELETE CASCADE;
What I'd like to do is make sure when I insert into Mixtime that user_id matches Spell & Ingredients' user_id fields
Pseudo code:
If (newMixtime.userId != Spell.user_id || newMixtime.userId != Ingredient.user_id) {
failHere
} else {
insert newMixtime into M
}
Note that this is not a join table. All three tables need to be query-able by the user_id field and table Mixtime has specific extra fields, it's just referencing Spell & Ingredient.
I could (and am currently) validating at the ORM layer by querying the db first, but this seems like something that should be possible in the DB layer and would save me trips.
If you know how to map this into Sequlize's Model syntax, that'd be grand, but I can probably figure that out if I have a pure postgres/SQL solution.

Answer 1

A fully normalized set of tables wouldn't have this constraint. The simplest way to represent this information is for every row in every table to be "owned" by exactly one row of exactly one parent table, as represented by a single foreign key. Unless you have a pressing need to share ingredients among different steps/spells of one user but NOT share them among different users, you don't need a user_id field on the ingredient.
Having true multi-table constraints (other than foreign keys) is extremely hard to do accurately and reliably. You can use triggers, but they tend to be very engine-specific, and I don't recommend putting your logic into triggers unless there's really no alternative.