rent migrate diff

Use rent migrate diff before creating or applying a migration. It loads rent/schema.rsl, inspects the live database, and writes the proposed operations to standard output without changing the database.

Preview executable SQL

rent migrate diff --database-url 'postgres://app:password@localhost/blog'

CREATE TABLE "public"."posts" ("author_id" bigint NOT NULL, "id" bigint GENERATED BY DEFAULT AS IDENTITY NOT NULL, "title" text NOT NULL, PRIMARY KEY ("id"));
CREATE TABLE "public"."users" ("id" bigint GENERATED BY DEFAULT AS IDENTITY NOT NULL, "name" text NOT NULL, PRIMARY KEY ("id"));
ALTER TABLE "public"."posts" ADD CONSTRAINT "posts_author_id_fkey" FOREIGN KEY ("author_id") REFERENCES "public"."users" ("id");

Rent renders one statement per line, exactly as it will be written to the migration file. Tables are created in name order and server databases add foreign keys afterwards; SQLite folds them into the table definition. Use SQL output for human review or to understand exactly what the backend will execute. Pass --format text for the classified summary that rent migrate preflight prints instead.

Use a schema in another package

rent migrate diff --to crates/blog/rent/schema.rsl

The default and custom paths both point to RSL sources. rent generate and the migration commands therefore share one source of truth.

Inspect semantic operations as JSON

rent migrate diff --database-url 'sqlite://local.db' --format json

{
  "operations": [
    {
      "CreateTable": {
        "schema": "main",
        "table": {
          "name": "users",
          "columns": [
            {
              "name": "id",
              "sql_type": "integer",
              "nullable": false,
              "size": null,
              "default": null,
              "generated": null,
              "identity": true
            }
          ],
          "primary_key": ["id"],
          "indexes": [],
          "foreign_keys": [],
          "checks": [],
          "triggers": [],
          "row_level_security": false,
          "policies": []
        }
      }
    }
  ]
}

Each operation carries the complete catalog object it creates or alters. JSON output is useful for migration policy checks, custom review tooling, or tests that should reason about an operation without parsing SQL.

Include removals explicitly

Objects that exist only in the live database are preserved by default. Include them in the plan only when removal is intentional:

rent migrate diff --drop-objects

DROP TABLE "legacy_sessions";

Review every destructive operation before proceeding. rent migrate apply still requires --allow-destructive before executing it.

Restrict PostgreSQL inspection

rent migrate diff --schemas public,audit

Use --schemas in databases where the application owns only a subset of PostgreSQL schemas.