Wrote first draft of sections database scheme

migrations/2021-09-13-143540_sections/down.sql

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+-- This file should undo anything in `up.sql`
+drop trigger insert_enforce_post_titles on posts;
+drop trigger update_enforce_post_titles on posts;
+drop function enforce_post_titles;
+
+drop table posts cascade;
+drop table sections cascade;

migrations/2021-09-13-143540_sections/up.sql

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+-- Your SQL goes here
+create table sections (
+    id uuid DEFAULT gen_random_uuid() PRIMARY KEY,
+
+    -- Title of the section
+    title varchar(255) UNIQUE NOT NULL,
+    -- Optional description of the section
+    description text,
+    -- Wether to show the section in the default list on the homepage
+    is_default boolean NOT NULL DEFAULT false,
+    -- Wether the posts should contain titles or not
+    has_titles boolean NOT NULL DEFAULT true
+);
+
+create table posts (
+    id uuid DEFAULT gen_random_uuid() PRIMARY KEY,
+
+    section_id uuid NOT NULL REFERENCES sections(id) ON DELETE CASCADE,
+    -- Title of the post
+    -- Wether this is NULL or not is enforced using the enforce_post_titles trigger
+    title varchar(255),
+    -- Post date, defaults to today
+    publish_date date NOT NULL DEFAULT now(),
+    -- Content of the post
+    content text NOT NULL
+);
+
+create function enforce_post_titles() returns trigger as $enforce_post_titles$
+    begin
+        -- Check for a wrongfully null title
+        if new.title is null and exists (
+            select 1 from sections where id = new.section_id and has_titles
+        ) then
+            raise exception 'Expected a post title, but got null.';
+        end if;
+
+        if new.title is not null and exists (
+            select 1 from sections where id = new.section_id and not has_titles
+        ) then
+            raise exception 'Expected an empty post title, but got a value.';
+        end if;
+
+        return new;
+    end;
+$enforce_post_titles$ language plpgsql;
+
+create trigger insert_enforce_post_titles
+    before insert on posts
+    for each row
+    execute function enforce_post_titles();
+
+create trigger update_enforce_post_titles
+    before update of title on posts
+    for each row
+    when (old.title is distinct from new.title)
+    execute function enforce_post_titles();