Setting Query Database Operation

Each Query object must have a database operation associated with it. The database operation determines what action to take when connecting to the database—from finding documents to storing them. There are two ways to assign a database operation to a Query object. One is to call the operation from the Model object and not specify a callback. The Query object returned has that operation assigned to it. For example:

var query =  model.find();

Once you already have a Query object, you can change the operation that is applied by calling the method on the Query object. For example, the following code creates a Query object that first applies a count() operation and then a find() operation. The where() clause is applied to both:

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var query =  model.count();
query.where('value').lt(5);
query.exec(function(){});
query.find();
query.exec(function(){});

This allows you to dynamically reuse the same Query object to perform multiple database operations. Table 16.2 lists the methods you can call on the Query object. You can also use these methods on a compiled Model object that can return a Query object by omitting the callback function. Keep in mind that if you pass in a callback function to any of these methods, the operation will be executed and the callback called when finished.

Table 16.2 Methods available on Query and Model objects to set database operation