team setting and postgres constraint

ops/migrations/20180916221309_constructs_table.js

@@ -1,18 +1,56 @@
+const team_size_trigger = `
+CREATE OR REPLACE FUNCTION enforce_team_size() RETURNS trigger AS $$
+DECLARE
+    team_size INTEGER := 3;
+    team_count INTEGER := 0;
+BEGIN
+    IF (TG_OP = 'UPDATE' OR TG_OP = 'INSERT') THEN
+        SELECT INTO team_count COUNT(id)
+        FROM constructs
+        WHERE account = NEW.account
+        AND team = true;
+    ELSIF (TG_OP = 'DELETE') THEN
+        SELECT INTO team_count COUNT(id)
+        FROM constructs
+        WHERE account = OLD.account
+        AND team = true;
+    END IF;
+
+    IF team_count != team_size THEN
+        RAISE EXCEPTION 'You must have exactly % constructs in your team.', team_size;
+    END IF;
+
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE CONSTRAINT TRIGGER check_team_size
+    AFTER INSERT OR UPDATE OR DELETE
+    ON constructs
+    DEFERRABLE INITIALLY DEFERRED
+    FOR EACH ROW
+    EXECUTE PROCEDURE enforce_team_size();
+`;
+
 exports.up = async knex => {
-    return knex.schema.createTable('constructs', table => {
+    await knex.schema.createTable('constructs', table => {
         table.uuid('id').primary();
         table.timestamps(true, true);
         table.uuid('account').notNullable()
         table.foreign('account')
-          .references('id')
-          .inTable('accounts')
-          .onDelete('CASCADE');
+            .references('id')
+            .inTable('accounts')
+            .onDelete('CASCADE');
         table.binary('data').notNullable();
 
         table.boolean('team')
-          .notNullable()
-          .defaultTo(false);
+            .notNullable()
+            .defaultTo(false);
     });
+
+    await knex.raw(team_size_trigger);
+
+    return true;
 };
 
-exports.down = async () => {};
+exports.down = async () => {};