Postgres create many to many relationship to table with composite primary key - postgresql

Question

CREATE TABLE "public"."Users" (
id SERIAL PRIMARY KEY NOT NULL,
name VARCHAR(255) NOT NULL,
email VARCHAR(255) UNIQUE NOT NULL,
"createdAt" TIMESTAMP NOT NULL DEFAULT now()
);
CREATE TABLE "public"."Boards" (
id SERIAL PRIMARY KEY NOT NULL,
name VARCHAR(255) NOT NULL,
"ownerId" SERIAL NOT NULL,
"createdAt" TIMESTAMP NOT NULL DEFAULT now(),
"updatedAt" TIMESTAMP,
FOREIGN KEY ("ownerId") REFERENCES "public"."Users"(id)
);
CREATE TABLE "public"."Board_Members"(
"userId" SERIAL,
"boardId" SERIAL,
CONSTRAINT board_member_pkey PRIMARY KEY ("userId", "boardId"),
FOREIGN KEY ("userId") REFERENCES "public"."Users"(id),
FOREIGN KEY ("boardId") REFERENCES "public"."Boards"(id)
);
CREATE TABLE "public"."Columns" (
id SERIAL PRIMARY KEY NOT NULL,
name VARCHAR(255) NOT NULL,
"boardId" SERIAL NOT NULL,
"createdAt" TIMESTAMP NOT NULL DEFAULT now(),
"updatedAt" TIMESTAMP,
FOREIGN KEY ("boardId") REFERENCES "public"."Boards"(id)
);
CREATE TABLE "public"."Cards" (
id SERIAL PRIMARY KEY NOT NULL,
name VARCHAR(255) NOT NULL,
description VARCHAR(255) NOT NULL,
dueDate TIMESTAMP,
"columnId" SERIAL NOT NULL,
"createdAt" TIMESTAMP NOT NULL DEFAULT now(),
"updatedAt" TIMESTAMP,
FOREIGN KEY ("columnId") REFERENCES "public"."Columns"(id),
);
I have these tables. Now I want to have a field called "assignee" in "Cards" table which will be a many-to-many relationship with "userId" from "Board_Members" table just like "Boards" and "Users" have a many-to-maany relationship. How do I do that? Do I create a new table and just reference the "userId" column as FK?

Answer 1

Just add a table with 2 foreign keys.
And because I think you want to switch the cards, from person to person. you could also want to keep track of the played history. See also the first normal form to check if your database is designed right.
https://en.wikipedia.org/wiki/First_normal_form
I hope I answered your question :)