Use of Criteria in Hibernate

I recently used Spring and Hibernate for development in the project. I feel that Criteria is easy to use, the query method <br> can be flexibly designed to assemble query conditions according to the features of Criteria. Now we will summarize the usage of Hibernate Criteria: <br> Hibernate designed CriteriaSpecification as the parent interface of Criteria. The following provides Criteria and DetachedCriteria. <Br> the major difference between Criteria and DetachedCriteria is that the creation method is different. Criteria is online. <br> it is created by Hibernate Session, while DetachedCriteria is offline, no <br> Session is required during creation. DetachedCriteria provides two static methods: forClass (Class) or forEntityName (Name) <br> to create a DetachedCriteria instance. The Spring framework provides the getHibernateTemplate <br> (). findByCriteria (detachedCriteria) method, which can easily return the query result based on DetachedCriteria <br>. <Br> both Criteria and DetachedCriteria can use Criterion and Projection to set query conditions. You can set <br> FetchMode (the mode of joint query capture) and set the sorting mode. For Criteria, you can also set FlushModel <br> and LockMode (database lock mode ). <Br> the following sections describe Criterion and Projection in detail. <Br> Criterion is the query condition of Criteria. Criteria provides the add (Criterion criterion) method to <br> add query conditions. <Br> the Criterion interface mainly includes Example, Junction, and SimpleExpression. <Br> the actual use of Junction is its two sub-classes conjunction AND disjunction, which use and or operator <br> to join the query condition set. <Br> Criterion instances can be created using the Restrictions tool class. Restrictions provides a large number of static <br> methods, such as eq (equal to) and ge (greater than or equal) create Criterion query conditions for methods such as between <br> (SimpleExpression instance ). In addition, Restrictions also provides methods to create conjunction and <br> disjunction instances by adding (Criteria) to the instance) method to add query conditions to form a set of query conditions <br>. <Br> As for the creation of Example, Example itself provides a static method create (Object <br> entity ), it is created based on an object (usually the object mapped to the database in actual use. Then you can set some <br> filter conditions: <br> Example exampleUser = Example. create (u) <br>. ignoreCase () // ignore case sensitivity <br>. enableLike (MatchMode. ANYWHERE); <br> // a String-type attribute that matches the value wherever it is located. Equivalent to % value % <br> the Project mainly enables Criteria to query reports and implement grouping. Project has three major implementations: <br> SimpleProjection, ProjectionList, and Property. SimpleProjection and <br> ProjectionList are instantiated by built-in Projections, for example, avg, count, max, <br> min, and sum can make it easy for developers to perform statistical queries on a field. <Br> & nbsp; Property is used to set query conditions for a field, such as Porperty. forName (& #8220; color & #8221 ;). in <br> (new String [] {& #8220; black & #8221;, & #8221; red & #8221;, & #8221; write & #8221;}); you can create a Project instance. Use the add (Project) method of <br> criteria to add it to the query condition. <Br> when using Criteria for query, it is important to note that Hibernate provides the classes and methods to meet the development query conditions. <br> The following describes how to create and assemble the query conditions: <br> 1. create a Criteria instance <br> org. hibernate. the Criteria interface indicates a query of a specific persistent class. Session is the factory of the Criteria instance. <Br> Criteria crit = sess. createCriteria (Cat. class); <br> crit. setMaxResults (50); <br> List cats = crit. list (); <br> 2. restrict result set content <br> A separate query condition is org. hibernate. criterion. an instance of the Criterion interface. <Br> the org. hibernate. criterion. Restrictions class defines factory methods for obtaining some built-in Criterion types. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. like ("name", "Fritz %") <br>. add (Restrictions. between ("weight", minWeight, maxWeight) <br>. list (); <br> constraints can be grouped by logic. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. like ("name", "Fritz %") <br>. add (Restrictions. or (<br> & nbsp; Restrictions. eq ("age", new Integer (0), <br> & nbsp; Restrictions. isNull ("age") <br>. list (); <br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. in ("name", new String [] {"Fritz", "Izi", "Pk"}) <br>. add (Restrictions. disjunction () <Br> & nbsp ;. add (Restrictions. isNull ("age") <br> & nbsp ;. add (Restrictions. eq ("age", new Integer (0) <br> & nbsp ;. add (Restrictions. eq ("age", new Integer (1) <br> & nbsp ;. add (Restrictions. eq ("age", new Integer (2) <br>. list (); <br> Hibernate provides many built-in criterion types (Restrictions subclass ), however, it is particularly useful to allow <br> you to use SQL directly. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. SQL ("lower ({alias }. name) like lower (?) "," Fritz % ", <br> Hibernate. STRING) <br>. list (); <br> {alias} placeholder should be replaced with the column alias of the queried object. <Br> A Property instance is another way to obtain a condition. You can call Property. forName () to create a <br> Property. <Br> Property age = Property. forName ("age"); <br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. disjunction () <br> & nbsp ;. add (age. isNull () <br> & nbsp ;. add (age. eq (new Integer (0) <br> & nbsp ;. add (age. eq (new Integer (1) <br> & nbsp ;. add (age. eq (new Integer (2) <br>. add (Property. forName ("name "). in (new String [] {"Fritz", "Izi", "Pk"}) <br>. list (); <B R> <br> 3. Result set sorting <br> you can use org. hibernate. criterion. Order to sort the query results. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. like ("name", "F %") <br>. addOrder (Order. asc ("name") <br>. addOrder (Order. desc ("age") <br>. setMaxResults (50) <br>. list (); <br> List cats = sess. createCriteria (Cat. class) <br>. add (Property. forName ("name "). like ("F %") <br>. addOrder (Property. forName ("name "). asc () <br>. addOrder (Property. forName ("age "). desc () <br>. s EtMaxResults (50) <br>. list (); <br> 4. association <br> you can use createCriteria () to easily create constraints between correlated entities. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. like ("name", "F %") <br>. createCriteria ("kittens") <br> & nbsp ;. add (Restrictions. like ("name", "F %") <br>. list (); <br> note that the second createCriteria () returns a new Criteria instance, which references elements in the kittens set. <Br> next, the replacement form is also useful in some cases. <Br> List cats = sess. createCriteria (Cat. class) <br>. createAlias ("kittens", "kt") <br>. createAlias ("mate", "mt") <br>. add (Restrictions. eqProperty ("kt. name "," mt. name ") <br>. list (); <br> (createAlias () does not create a new Criteria instance .) <Br> the kittens set returned by the previous two queries stored by the Cat instance is not pre-filtered by the condition. If you want to obtain only <br> qualified kittens, you must use returnMaps (). <Br> List cats = sess. createCriteria (Cat. class) <br>. createCriteria ("kittens", "kt") <br>. add (Restrictions. eq ("name", "F %") <br>. returnMaps () <br>. list (); <br> Iterator iter = cats. iterator (); <br> while (iter. hasNext () {<br> Map map = (Map) iter. next (); <br> Cat cat = (Cat) map. get (Criteria. ROOT_ALIAS); <br> Cat kitten = (Cat) map. get ("kt"); <br >}< br> <br> 5. dynamic Association crawling <br> you can use setFetchMode () to run Defines the semantics of Dynamic Association capture. <Br> List cats = sess. createCriteria (Cat. class) <br>. add (Restrictions. like ("name", "Fritz %") <br>. setFetchMode ("mate", FetchMode. EAGER) <br>. setFetchMode ("kittens", FetchMode. EAGER) <br>. list (); <br> This query can capture mate and kittens through external connections. <Br> 6. query Example <br> org. hibernate. criterion. Example class allows you to construct a conditional query using a given instance. <Br> Cat cat = new Cat (); <br> cat. setSex ('F'); <br> cat. setColor (Color. BLACK); <br> List results = session. createCriteria (Cat. class) <br>. add (Example. create (cat) <br>. list (); <br> Version attributes, identifiers, and associations are ignored. By default, null attributes are excluded. <Br> You can adjust Example to make it more practical. <Br> Example example = Example. create (cat) <br>. excludeZeroes () & nbsp; // exclude zero valued properties <br>. excludeProperty ("color") // exclude the property named "color" <br>. ignoreCase () & nbsp; // perform case insensitive string comparisons <br>. enableLike (); & nbsp; // use like for string comparisons <br> List results = session. createCriteria (Cat. class) <br>. ad D (example) <br>. list (); <br> You can even use examples to place conditions on the correlated object. <Br> List results = session. createCriteria (Cat. class) <br>. add (Example. create (cat) <br>. createCriteria ("mate") <br> & nbsp ;. add (Example. create (cat. getMate () <br>. list (); <br> 7. projections, aggregation, and grouping <br> org. hibernate. criterion. projections is the instance factory of Projection. We call <br> setProjection () to project a query. <Br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. rowCount () <br>. add (Restrictions. eq ("color", Color. BLACK) <br>. list (); <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. projectionList () <br> & nbsp ;. add (Projections. rowCount () <br> & nbsp ;. add (Projections. avg ("weight") <br> & nbsp ;. add (Projections. max ("weight ")) <Br> & nbsp ;. add (Projections. groupProperty ("color") <br>. list (); <br> you do not need to explicitly use "group by" in a condition query ". Some projection types are defined as group projection. <br> they also appear in the group by clause of SQL. <Br> you can assign an alias to a projection so that the projection values are constrained or referenced by sorting. The following are two different <br> Implementation Methods: <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. alias (Projections. groupProperty ("color"), "colr") <br>. addOrder (Order. asc ("colr") <br>. list (); <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. groupProperty ("color "). as ("colr") <br>. addOrder (Order. asc ("colr") <br>. list (); <br> <B R> the alias () and as () methods can easily package a Projection instance into a Projection instance of another alias. In short, <br> when you add a projection to a projection List, you can specify an alias for it: <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. projectionList () <br> & nbsp ;. add (Projections. rowCount (), "catCountByColor") <br> & nbsp ;. add (Projections. avg ("weight"), "avgWeight") <br> & nbsp ;. add (Projections. max ("weight"), "maxWeight") <br> & nbsp ;. add (Projections. groupProperty ("color"), "color") <br>. AddOrder (Order. desc ("catCountByColor") <br>. addOrder (Order. desc ("avgWeight") <br>. list (); <br> List results = session. createCriteria (Domestic. class, "cat") <br>. createAlias ("kittens", "kit") <br>. setProjection (Projections. projectionList () <br> & nbsp ;. add (Projections. property ("cat. name ")," catName ") <br> & nbsp ;. add (Projections. property ("kit. name ")," kitName ") <br>. addOrder (Order. asc ("catName") <br>. addOrder (Order. asc ("kitName") <br>. list (); <br> you can also use Property. forName () indicates projection: <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Property. forName ("name") <br>. add (Property. forName ("color "). eq (Color. BLACK) <br>. list (); <br> List results = session. createCriteria (Cat. class) <br>. setProjection (Projections. projectionList () <br> & nbsp;. Add (Projections. rowCount (). as ("catCountByColor") <br> & nbsp ;. add (Property. forName ("weight "). avg (). as ("avgWeight") <br> & nbsp ;. add (Property. forName ("weight "). max (). as ("maxWeight") <br> & nbsp ;. add (Property. forName ("color "). group (). as ("color") <br>. addOrder (Order. desc ("catCountByColor") <br>. addOrder (Order. desc ("avgWeight") <br>. list (); <br> 8. offline (detached) query and subquery <br> D The etachedCriteria class allows you to create a query outside the range of a session and use any Session to <br> execute it. <Br> DetachedCriteria query = DetachedCriteria. forClass (Cat. class) <br>. add (Property. forName ("sex "). eq ('F'); <br> // create a Session <br> Session session = .; <br> Transaction txn = session. beginTransaction (); <br> List results = query. getExecutableCriteria (session ). setMaxResults (100 ). list (); <br> txn. commit (); <br> session. close (); <br> DetachedCriteria can also be used to represent subqueries. The condition instance contains Subqueries that can be obtained through Subqueries or <br> Property. <Br> DetachedCriteria avgWeight = DetachedCriteria. forClass (Cat. class) <br>. setProjection (Property. forName ("weight "). avg (); <br> session. createCriteria (Cat. class) <br>. add (Property. forName ("weight ). gt (avgWeight) <br>. list (); <br> DetachedCriteria weights = DetachedCriteria. forClass (Cat. class) <br>. setProjection (Property. forName ("weight"); <br> session. createCriteria (Cat. class) <br>. add (Subqueries. geAll ("weight", weights) <br>. list (); <br> associated subqueries are also possible: <br> DetachedCriteria avgWeightForSex = DetachedCriteria. forClass (Cat. class, "cat2") <br>. setProjection (Property. forName ("weight "). avg () <br>. add (Property. forName ("cat2.sex "). eqProperty ("cat. sex "); <br> session. createCriteria (Cat. class, "cat") <br>. add (Property. forName ("weight ). gt (avgWeightForSex) <br>. list (); <br> supplement: <br> criteria. add (Expression. eq ("status", new Integer (status); <br> criteria. add (Expression. in ("status", optParm. getQueryStatus (); <br> <a href = "http://hi.baidu.com/1166824/blog/item/a66c053ef9e9ffea55e72338.html