datatable.directory/database/migrations/2018_07_08_194000_create_proposals_table.php

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateProposalsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('proposals', function (Blueprint $table) {
            $table->increments('id');
            $table->timestamps();

            // note that a revision may be shared by multiple tables, thus a proposal may also apply to different tables

            $table->unsignedInteger('table_id')->index()->nullable(); // table this proposal was written for
            $table->unsignedInteger('revision_id')->index(); // parent revision (applying it to a different revisions may cause conflicts)
            $table->unsignedInteger('author_id')->index();

            $table->text('note')->nullable();

            $table->jsonb('changes'); // the actual meat of the changeset is stored here

            $table->foreign('revision_id')->references('id')->on('revisions')
                ->onDelete('cascade'); // a proposal without the revision is useless

            // deleting the table must NOT delete the proposals, as they may be applicable to forks sharing the revision
            $table->foreign('table_id')->references('id')->on('tables')
                ->onDelete('set null');

            // deleting author wipes their proposals
            $table->foreign('author_id')->references('id')->on('users')
                ->onDelete('cascade');
        });

        // add FK to revisions to point to the source proposal
        Schema::table('revisions', function (Blueprint $table) {
            $table->foreign('proposal_id')->references('id')->on('proposals')
                ->onDelete('set null');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        // remove the FK
        Schema::table('revisions', function (Blueprint $table) {
            $table->dropForeign('revisions_proposal_id_foreign');
        });

        Schema::dropIfExists('proposals');
    }
}