NHibernate-CreateCriteria与CreateAlias

问题描述

假定以下情况:

class Project{
   public Job Job;
}

class Job{
   public Name;
}

假设我想使用Criteria API搜索Job名称为"sumthing"的所有项目.

Assuming I want to use the Criteria API to search for all projects whose Job has the name "sumthing".

我可以使用CreateAlias为Job创建一个别名并使用它来访问Name，也可以为Job属性创建一个新的Criteria并按Name搜索.

I could use the CreateAlias to create an alias for Job and use it to access Name, or I could create a new Criteria for the property Job and search by Name.

明智的选择，有什么区别吗?

Performance wise, is there any difference?

推荐答案

鉴于这些要求没有区别，生成的SQL是相同的:用于映射:

given these requirements there would be no difference, the generated SQL is the same:for mappings:

    <?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
    <class name="Project" table="Project">
        <id name="Id" type="Int32" unsaved-value="0">
            <column name="Id" sql-type="int" not-null="true" unique="true"/>
            <generator class="native" />
        </id>
        <many-to-one name="Job" column="FK_JobId" cascade="save-update" not-null="true" />
    </class>
</hibernate-mapping>
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
    <class name="Job" table="Job">
        <id name="Id" type="Int32" unsaved-value="0">
            <column name="Id" sql-type="int" not-null="true" unique="true"/>
            <generator class="native" />
        </id>
        <property name="Name" type="String">
            <column name="Name" sql-type="nvarchar" length="50" not-null="true"/>
        </property>
    </class>
</hibernate-mapping>

和类

public class Project
    {
        public Project() { }

        public virtual int Id { get; set; }

        public virtual Job Job { get; set; }
    }
public class Job
    {
        public Job() { }

        public virtual int Id { get; set; }

        public virtual String Name { get; set; }
    }

这些条件定义

ICriteria criteriacrit = session
  .CreateCriteria(typeof (Project))
  .CreateCriteria("Job", "job")
  .Add(Restrictions.Eq("job.Name", "sometextA"));

ICriteria aliascrit = session
  .CreateCriteria(typeof (Project))
  .CreateAlias("Job", "job")
  .Add(Restrictions.Eq("job.Name", "sometextB"));

生成相同的SQL

SELECT
  this_.Id as Id2_1_,
  this_.FK_JobId as FK2_2_1_,
  job1_.Id as Id1_0_,
  job1_.Name as Name1_0_
FROM
  Project this_
  inner join Job job1_
    on this_.FK_JobId=job1_.Id
WHERE job1_.Name = @p0; @p0 = 'sometextA'

SELECT
  this_.Id as Id2_1_,
  this_.FK_JobId as FK2_2_1_,
  job1_.Id as Id1_0_,
  job1_.Name as Name1_0_
FROM
  Project this_
  inner join Job job1_
    on this_.FK_JobId=job1_.Id
WHERE job1_.Name = @p0; @p0 = 'sometextB'

但是请注意，CreateAlias依赖于映射来生成关联，而CreateCriteria调用允许指定JoinType.

note however that the CreateAlias relies on the mappings to generate associations whereas the CreateCriteria call allows to specify JoinType.

所以，这些电话

ICriteria criteriacrit = session
  .CreateCriteria(typeof(Project))
  .CreateCriteria("Job",JoinType.LeftOuterJoin)
  .Add(Restrictions.Eq("Name", "sometextA"));

ICriteria aliascrit = session
  .CreateCriteria(typeof (Project))
  .CreateAlias("Job", "job")
  .Add(Restrictions.Eq("job.Name", "sometextB"));

生成这些SQL语句

SELECT
  this_.Id as Id2_1_,
  this_.FK_JobId as FK2_2_1_,
  job1_.Id as Id1_0_,
  job1_.Name as Name1_0_
FROM
  Project this_
  **left outer** join Job job1_
    on this_.FK_JobId=job1_.Id
WHERE job1_.Name = @p0; @p0 = 'sometextA'

SELECT
  this_.Id as Id2_1_,
  this_.FK_JobId as FK2_2_1_,
  job1_.Id as Id1_0_,
  job1_.Name as Name1_0_
FROM Project this_
  **inner join** Job job1_
    on this_.FK_JobId=job1_.Id
WHERE job1_.Name = @p0; @p0 = 'sometextB'

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