What does laravel attach return?

Laravel is a dynamic PHP framework that provides many convenient features to speed up development. The attach method is a common method in Eloquent ORM, which is used to add an association relationship to a model. Its return value has always been a problem that troubles developers.

First, let’s take a look at the syntax of the attach method:

$relatedIds = [1, 2, 3];
$model->relation()->attach($relatedIds);

In this example, $model represents the local model, and relation() represents an associated model. The parameter of the attach() method is an array, used to add one or more existing associated models. Specifically, this method will insert a new set of records into the association table. The records include a local model ID and an associated model ID.

So, what is the return value of the attach method? I believe many people think that the attach method returns new records inserted into the related table, but in fact, it is not like this. The attach method actually returns an integer or an empty collection, depending on how many insert operations were performed.

If the attach method performs only one insertion operation, then it will return the ID of the newly inserted record. This ID is an integer, which represents the ID of the new record just inserted in the related table. However, if the attach method performs multiple insertion operations, it will return an empty IlluminateDatabaseEloquentCollection object, which is an empty collection. This collection object is the same as the Collection object of other Eloquent model instances, and all the same methods can be used, such as count(), first(), etc.

Regarding the return value of the attach method, some developers may ask: Since the return value is just an integer or an empty set, can we ignore the return value? The answer to this question is also simple. Although you can ignore the return value of this method, we do not recommend doing so. In fact, the return value can provide some important information to our code.

If the attach method returns an integer, then it indicates that the insertion operation was successful, and the returned integer is the ID of the newly inserted record in the associated table. We can use this ID to operate on newly inserted records in subsequent code. If the attach method returns an empty collection, the insertion failed and we need to handle the failure.

To summarize, the attach method is a very commonly used method in Laravel. Its function is to insert a new set of records into the associated table, and its return value depends on how many insert operations have been performed. If only one insert operation is performed, then it will return the ID of the newly inserted record; if multiple insert operations are performed, then it will return an empty collection. We recommend not to ignore the return value of this method as it can provide us with some important information.

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