5.4.3 Criteria - Reference Documentation
Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith
Version: 2.0.4
5.4.3 Criteria
Criteria is an advanced way to query that uses a Groovy builder to construct potentially complex queries. It is a much better approach than building up query strings using aStringBuffer.Criteria can be used either with the createCriteria or withCriteria methods. The builder uses Hibernate's Criteria API. The nodes on this builder map the static methods found in the Restrictions class of the Hibernate Criteria API. For example:def c = Account.createCriteria()
def results = c {
between("balance", 500, 1000)
eq("branch", "London")
or {
like("holderFirstName", "Fred%")
like("holderFirstName", "Barney%")
}
maxResults(10)
order("holderLastName", "desc")
}Account objects in a List matching the following criteria:
balanceis between 500 and 1000branchis 'London'holderFirstNamestarts with 'Fred' or 'Barney'
holderLastName.If no records are found with the above criteria, an empty List is returned.Conjunctions and Disjunctions
As demonstrated in the previous example you can group criteria in a logical OR using anor { } block:or {
between("balance", 500, 1000)
eq("branch", "London")
}and {
between("balance", 500, 1000)
eq("branch", "London")
}not {
between("balance", 500, 1000)
eq("branch", "London")
}Querying Associations
Associations can be queried by having a node that matches the property name. For example say theAccount class had many Transaction objects:class Account {
…
static hasMany = [transactions: Transaction]
…
}transaction as a builder node:def c = Account.createCriteria()
def now = new Date()
def results = c.list {
transactions {
between('date', now - 10, now)
}
}Account instances that have performed transactions within the last 10 days.
You can also nest such association queries within logical blocks:def c = Account.createCriteria()
def now = new Date()
def results = c.list {
or {
between('created', now - 10, now)
transactions {
between('date', now - 10, now)
}
}
}Querying with Projections
Projections may be used to customise the results. Define a "projections" node within the criteria builder tree to use projections. There are equivalent methods within the projections node to the methods found in the Hibernate Projections class:def c = Account.createCriteria()def numberOfBranches = c.get {
projections {
countDistinct('branch')
}
}Using SQL Restrictions
You can access Hibernate's SQL Restrictions capabilities.def c = Person.createCriteria()def peopleWithShortFirstNames = c.list {
sqlRestriction "char_length(first_name) <= 4"
}Note that the parameter there is SQL. Thefirst_nameattribute referenced in the example refers to the persistence model, not the object model like in HQL queries. ThePersonproperty namedfirstNameis mapped to thefirst_namecolumn in the database and you must refer to that in thesqlRestrictionstring.Also note that the SQL used here is not necessarily portable across databases.
Using Scrollable Results
You can use Hibernate's ScrollableResults feature by calling the scroll method:def results = crit.scroll {
maxResults(10)
}
def f = results.first()
def l = results.last()
def n = results.next()
def p = results.previous()def future = results.scroll(10)
def accountNumber = results.getLong('number')A result iterator that allows moving around within the results by arbitrary increments. The Query / ScrollableResults pattern is very similar to the JDBC PreparedStatement/ ResultSet pattern and the semantics of methods of this interface are similar to the similarly named methods on ResultSet.Contrary to JDBC, columns of results are numbered from zero.
Setting properties in the Criteria instance
If a node within the builder tree doesn't match a particular criterion it will attempt to set a property on the Criteria object itself. This allows full access to all the properties in this class. This example callssetMaxResults and setFirstResult on the Criteria instance:import org.hibernate.FetchMode as FM … def results = c.list { maxResults(10) firstResult(50) fetchMode("aRelationship", FM.JOIN) }
Querying with Eager Fetching
In the section on Eager and Lazy Fetching we discussed how to declaratively specify fetching to avoid the N+1 SELECT problem. However, this can also be achieved using a criteria query:def criteria = Task.createCriteria()
def tasks = criteria.list{
eq "assignee.id", task.assignee.id
join 'assignee'
join 'project'
order 'priority', 'asc'
}join method: it tells the criteria API to use a JOIN to fetch the named associations with the Task instances. It's probably best not to use this for one-to-many associations though, because you will most likely end up with duplicate results. Instead, use the 'select' fetch mode:
import org.hibernate.FetchMode as FM … def results = Airport.withCriteria { eq "region", "EMEA" fetchMode "flights", FM.SELECT }
flights association, you will get reliable results - even with the maxResults option.An important point to bear in mind is that if you include associations in the query constraints, those associations will automatically be eagerly loaded. For example, in this query:fetchModeandjoinare general settings of the query and can only be specified at the top-level, i.e. you cannot use them inside projections or association constraints.
def results = Airport.withCriteria {
eq "region", "EMEA"
flights {
like "number", "BA%"
}
}flights collection would be loaded eagerly via a join even though the fetch mode has not been explicitly set.Method Reference
If you invoke the builder with no method name such as:c { … }c.list { … }| Method | Description |
|---|---|
| list | This is the default method. It returns all matching rows. |
| get | Returns a unique result set, i.e. just one row. The criteria has to be formed that way, that it only queries one row. This method is not to be confused with a limit to just the first row. |
| scroll | Returns a scrollable result set. |
| listDistinct | If subqueries or associations are used, one may end up with the same row multiple times in the result set, this allows listing only distinct entities and is equivalent to DISTINCT_ROOT_ENTITY of the CriteriaSpecification class. |
| count | Returns the number of matching rows. |

