# `Bylaw.Db.Adapters.Postgres.Checks.MissingForeignKeyConstraints`
[🔗](https://github.com/ryanzidago/bylaw/blob/v0.1.0-alpha.1/lib/bylaw/db/adapters/postgres/checks/missing_foreign_key_constraints.ex#L1)

Flags Postgres columns that look like foreign keys but have no constraint.

## Examples

Before, `account_id` looks like a relationship but the database does not
enforce it:

```sql
CREATE TABLE orders (
  id uuid PRIMARY KEY,
  account_id uuid NOT NULL
);
```

Application code can insert orphaned `orders.account_id` values, and bugs may
only surface later as missing joins or cleanup problems.

After, make the relationship explicit in Postgres:

```sql
CREATE TABLE orders (
  id uuid PRIMARY KEY,
  account_id uuid NOT NULL REFERENCES accounts(id)
);
```

The database now rejects orphaned rows no matter which code path writes to the
table.

## Notes

This check does not infer relationships from column names that do not end in
`_id`, and it does not validate whether the referenced table name matches the
column name. It only checks whether a candidate column is covered by a
Postgres foreign key constraint.

## Options

By default the check inspects all non-system schemas in a Postgres target.
Use `schemas: [...]` or `tables: [...]` for simple filtering:

```elixir
{Bylaw.Db.Adapters.Postgres.Checks.MissingForeignKeyConstraints,
 schemas: ["public"],
 tables: ["orders", "line_items"]}
```

Use `rules: [...]` when the scope needs column matchers or exclusions:

```elixir
{Bylaw.Db.Adapters.Postgres.Checks.MissingForeignKeyConstraints,
 rules: [
   [
     only: [schema: "public"],
     except: [
       [table: "events", column: "actor_id"],
       [column: ~r/_external_id$/]
     ]
   ]
 ]}
```

A column is treated as a candidate when it ends in `_id`, is not named `id`,
is not part of a primary key, and is not covered by a declared foreign key
constraint.

## Usage

Add this module to the checks passed to
`Bylaw.Db.Adapters.Postgres.validate/2`. See the
[README usage section](readme.html#usage) for the full ExUnit setup.

# `check_opt`

```elixir
@type check_opt() :: {:validate, boolean()} | {:rules, [keyword()]}
```

# `check_opts`

```elixir
@type check_opts() :: [check_opt()]
```

# `validate`

```elixir
@spec validate(target :: Bylaw.Db.Target.t(), opts :: check_opts()) ::
  Bylaw.Db.Check.result()
```

Implements the `Bylaw.Db.Check` validation callback.

---

*Consult [api-reference.md](api-reference.md) for complete listing*