Doctrine provides a QueryBuilder interface to build queries for MongoDB. Given that we have defined our models as described in Chapter 2, Schema Design and Data Modeling, we can do this to obtain an instance of a QueryBuilder interface named $db, get a default find-all query, and execute it, as follows:
$qb = $dm->createQueryBuilder('Book');
$query = $qb->getQuery();
$books = $query->execute();
The $books variable now contains an iterable lazy data-loading cursor over our result set.
Using $qb->eagerCursor(true); over the QueryBuilder object will return an eager cursor, fetching all data from MongoDB as soon as we start iterating our results.
Some helper methods for querying are listed here:
- ->getSingleResult(): This is equivalent to findOne().
- ->select('name'): This returns only the values for the 'key' attribute from our books collection. ObjectId will always be returned.
- ->hint('book_name_idx'): This forces the query to use this index. We'll see more about indexes in Chapter 7, Indexing.
- ->distinct('name'): This returns distinct results by name.
- ->limit(10): This returns the first 10 results.
- ->sort('name', 'desc'): This sorts by name (such as desc or asc).
Doctrine uses the concept of hydration when fetching documents from MongoDB. Hydration defines the query's result schema. We can, for example, configure hydration to return a collection of objects, a single scalar value, or an array of arrays representing different records. Using an identity map, it will cache MongoDB results in memory and consult this map before hitting the database. Disabling hydration can be done per query by using ->hydration(false), or globally using the configuration as explained in Chapter 2, Schema Design and Data Modeling.
We can also force Doctrine to refresh data in the identity map for a query from MongoDB using ->refresh() on $qb.
The comparison operators that we can use with Doctrine are as follows:
- where($javascript)
- in($values)
- notIn($values)
- equals($value)
- notEqual($value)
- gt($value)
- gte($value)
- lt($value)
- lte($value)
- range($start, $end)
- size($size)
- exists($bool)
- type($type)
- all($values)
- mod($mod)
- addOr($expr)
- addAnd($expr)
- references($document)
- includesReferenceTo($document)
Consider the following query as an example:
$qb = $dm->createQueryBuilder('Book')
->field('price')->lt(30);
This will return all books whose price is less than 30.
addAnd() may seem redundant since chaining multiple query expressions in Doctrine is implicitly AND, but it is useful if we want to do AND ( (A OR B), (C OR D) ) where A, B, C, and D are standalone expressions.
To nest multiple OR operators with an external AND query, and in other equally complex cases, the nested ORs need to be evaluated as expressions using ->expr():
$expression = $qb->expr()->field('name')->equals('MongoDB with Doctrine')
$expression is a standalone expression that can be used with $qb->addOr($expression) and similarly with addAnd().