ecto_extract_migrations

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ecto_extract_migrations

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Elixir library to generate Ecto migrations from a PostgreSQL schema SQL file. Uses NimbleParsec and macro-style code generation.

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# ecto_extract_migrations

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Mix task to generate Ecto migrations from a Postgres schema SQL file.

This lets you take an existing project and move it into Elixir
with a proper development workflow.

## Usage

1. Generate a schema-only dump of the database to SQL:

```shell
   pg_dump --schema-only --no-owner postgres://dbuser:dbpassword@localhost/dbname > dbname.schema.sql
   ```

2. Generate migrations from the SQL file:

```shell
   mix ecto.extract.migrations --sql-file dbname.schema.sql
   ```

or, from outside the target project:

```shell
   mix ecto.extract.migrations --sql-file dbname.schema.sql --repo "MyProject.Repo" --migrations-path ../myproject/priv/repo/migrations
   ```

3. Create a test database, run migrations to create the schema, then
export it and verify that it matches the original database:

```shell
   createuser --encrypted --pwprompt dbuser
   dropdb dbname_migrations
   createdb -Odbuser -Eutf8 dbname_migrations

mix ecto.migrate --log-sql

pg_dump --schema-only --no-owner postgres://dbuser@localhost/dbname_migrations > dbname_migrations.sql

cat dbname.schema.sql | grep -v -E '^--|^$' > old.sql
   cat dbname_migrations.sql | grep -v -E '^--|^$' > new.sql
   diff -wu old.sql new.sql
   ```

## Details

This was written to migrate a legacy database with hundreds of tables and
objects.

The parser uses [NimbleParsec](https://github.com/dashbitco/nimble_parsec), and
is based on the SQL grammar, so it is precise (unlike regex) and reasonably
complete. It doesn't support every esoteric option, just what we needed, but
that was quite a lot. Patches are welcome.

Supports:

* `ALTER SEQUENCE`
* `ALTER TABLE`
* `CREATE EXTENSION`
* `CREATE FUNCTION`
* `CREATE INDEX`
* `CREATE SCHEMA`
* `CREATE SEQUENCE`
* `CREATE TABLE`
* `CREATE TRIGGER`
* `CREATE TYPE`
* `CREATE VIEW`

## Installation

Add `ecto_extract_migrations` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:ecto_extract_migrations, "~> 0.1.0"}
  ]
end
```

## Resources

Here are some useful resources for NimbleParsec:

* https://stefan.lapers.be/posts/elixir-writing-an-expression-parser-with-nimble-parsec/
* https://github.com/slapers/ex_sel

## Alternatives

* [ecto_generator](https://github.com/pmarreck/ecto_generator) generates Ecto schemas by querying
  the database [information schema](https://www.postgresql.org/docs/13/information-schema.html)
* [ex_abnf](https://github.com/marcelog/ex_abnf) generates a parser based on an
  [ABNF grammar](https://en.wikipedia.org/wiki/Augmented_Backus%E2%80%93Naur_form).

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