# Querying Relationships

When querying an entity, you may want to restrict the query based on the existence or absence of a related entity.  You can do that using the following four methods:

## has

| Name             | Type    | Required | Default | Description                                                                           |
| ---------------- | ------- | -------- | ------- | ------------------------------------------------------------------------------------- |
| relationshipName | String  | `true`   |         | The relationship to check.  Can also be a dot-delimited list of nested relationships. |
| operator         | String  | `false`  |         | An optional operator to constrain the check. See qb for a list of valid operators.    |
| count            | numeric | `false`  |         | An optional count to constrain the check.                                             |
| negate           | boolean | `false`  | `false` | If true, checks for the the absence of the relationship instead of its existence.     |

Checks for the existence of a relationship when executing the query.

By default, a `has` constraint will only return entities that have one or more of the related entity.

```javascript
getInstance( "User" ).has( "posts" ).get();
```

An optional operator and count can be added to the call.

```javascript
getInstance( "User" ).has( "posts", ">", 2 ).get();
```

Nested relationships can be checked by passing a dot-delimited string of relationships.

```javascript
getInstance( "User" ).has( "posts.comments" ).get();
```

## doesntHave

| Name             | Type    | Required | Default | Description                                                                           |
| ---------------- | ------- | -------- | ------- | ------------------------------------------------------------------------------------- |
| relationshipName | String  | `true`   |         | The relationship to check.  Can also be a dot-delimited list of nested relationships. |
| operator         | String  | `false`  |         | An optional operator to constrain the check. See qb for a list of valid operators.    |
| count            | numeric | `false`  |         | An optional count to constrain the check.                                             |

Checks for the absence of a relationship when executing the query.

By default, a `doesntHave` constraint will only return entities that have zero of the related entity.

```javascript
getInstance( "User" ).doesntHave( "posts" ).get();
```

An optional operator and count can be added to the call.

```javascript
getInstance( "User" ).doesntHave( "posts", "<=", 1 ).get();
```

Nested relationships can be checked by passing a dot-delimited string of relationships.

```javascript
getInstance( "User" ).doesntHave( "posts.comments" ).get();
```

## whereHas

| Name             | Type     | Required | Default | Description                                                                           |
| ---------------- | -------- | -------- | ------- | ------------------------------------------------------------------------------------- |
| relationshipName | String   | `true`   |         | The relationship to check.  Can also be a dot-delimited list of nested relationships. |
| closure          | Function | `true`   |         | A closure to constrain the relationship check.                                        |
| operator         | String   | `false`  |         | An optional operator to constrain the check. See qb for a list of valid operators.    |
| count            | numeric  | `false`  |         | An optional count to constrain the check.                                             |
| negate           | boolean  | `false`  | `false` | If true, checks for the the absence of the relationship instead of its existence.     |

When you need to have more control over the relationship constraint, you can use `whereHas`.  This method operates similarly to `has` but also accepts a callback to configure the relationship constraint.

The `whereHas` callback is passed a builder instance configured according to the relationship.  You may call any entity or query builder methods on it as usual.

```javascript
getInstance( "User" )
    .whereHas( "posts", function( q ) {
	      q.where( "body", "like", "%different%" );
    } )
		.get();
```

When you specify a nested relationship, the builder instance is configured for the last relationship specified.

```javascript
getInstance( "User" )
    .whereHas( "posts.comments", function( q ) {
	      q.where( "body", "like", "%great%" );
	  } )
	  .get();
```

An optional operator and count can be added to the call, as well.

```javascript
getInstance( "User" )
    .whereHas( "posts.comments", function( q ) {
	      q.where( "body", "like", "%great%" );
	  }, ">", 2 )
	  .get();
```

## whereDoesntHave

| Name             | Type     | Required | Default | Description                                                                           |
| ---------------- | -------- | -------- | ------- | ------------------------------------------------------------------------------------- |
| relationshipName | String   | `true`   |         | The relationship to check.  Can also be a dot-delimited list of nested relationships. |
| closure          | Function | `true`   |         | A closure to constrain the relationship check.                                        |
| operator         | String   | `false`  |         | An optional operator to constrain the check. See qb for a list of valid operators.    |
| count            | numeric  | `false`  |         | An optional count to constrain the check.                                             |

The `whereDoesntHave` callback is passed a builder instance configured according to the relationship.  You may call any entity or query builder methods on it as usual.

```javascript
getInstance( "User" )
    .whereDoesntHave( "posts", function( q ) {
	      q.where( "body", "like", "%different%" );
    } )
		.get();
```

When you specify a nested relationship, the builder instance is configured for the last relationship specified.

```javascript
getInstance( "User" )
    .whereDoesntHave( "posts.comments", function( q ) {
	      q.where( "body", "like", "%great%" );
	  } )
	  .get();
```

An optional operator and count can be added to the call, as well.

```javascript
getInstance( "User" )
    .whereDoesntHave( "posts.comments", function( q ) {
	      q.where( "body", "like", "%great%" );
	  }, ">", 2 )
	  .get();
```