# Foreign key snippets

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{% tab title="Foreign Keys - Add" %}
Whalesync supports foreign keys. After creating your tables, you can designate a foreign key and then point it to another table's primary key.

```sql
ALTER TABLE public."Table"
ADD CONSTRAINT table_category_fkey
FOREIGN KEY ("category")
REFERENCES categories("name");
```

In the example above we are adding to a table called "Table" to an existing column called "category" a foreign key pointing to column called "name" in a table called "categories". The example creates the foreign key relationship, it does not create any tables and columns, they must already all exist.
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{% tab title="Foreign Keys - Arrays" %}
**About foreign key arrays**

Unfortunately, Postgres does not support arrays of foreign keys. Some of the other apps we connect with (e.g. Airtable) do, so we've tried to build a workaround for this. With this workaround you'll be able to sync Airtable linked records with a fake Postgres foreign key array.

**How it works**

At a high-level, you can configure a Postgres column to be an array BUT signal to Whalesync that you'd like us to treat it as a foreign key array.

Since Postgres just sees this as an array, the field no longer has the same validation, but it will sync.

{% hint style="info" %}
**Note:** a bad value here will not break Whalesync, that value will simply not sync until you correct it. 
{% endhint %}

**How do I implement this?**

Imagine you have two tables:

* Contacts
* Company

To create a foreign key array you can:

1. Ensure both tables have a primary key (e.g. uuid)
2. In Company,  create an array column "People\_fk\_Contacts" with type uuid\[] to match the type of the table id.

   1. The "\_fk" designates to Whalesync that you want this to be a foreign key.
   2. The "\_Contacts" designates that it should point to the Contacts table.

   (\*note - must match capitlization)
3. Set up your sync in Whalesync as normal, mapping your fields.

**Example snippet**

```sql
CREATE TABLE public."Contacts" (
"id" uuid PRIMARY KEY DEFAULT gen_random_uuid(),
"Email" text );

CREATE TABLE public."Company" (
"id" uuid PRIMARY KEY DEFAULT gen_random_uuid(),
"Name" text,
"People_fk_Contacts" uuid[] );
```

{% endtab %}
{% endtabs %}