NHibernate - CreateCriteria vs CreateAlias

Question

假设以下场景：

class Project{
   public Job Job;
}

class Job{
   public Name;
}

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

我可以使用CreateAlias为工作创建一个别名，并使用它访问名称，或者我可以为属性工作创建一个新的条件，并按名称进行搜索。

性能方面，有什么不同吗？

Answer 1

考虑到这些需求没有区别，生成的SQL是相同的:对于映射：

    <?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; }
    }

这些标准定义

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。

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'

Answer 2

为了解释NHibernate 2.0 +中CreateCriteria和CreateAlias之间的区别，让我们看看下面的域模型。

public class Product
{
    public virtual int Id { get; private set; }
    public virtual string Name { get; set; }
    public virtual decimal Price { get; set; }
    public virtual Category Category { get; set; }
    public virtual IList<ProductStock> ProductStocks { get; set; }
}

public class Category
{
    public virtual int Id { get; private set; }
    public virtual string Name { get; set; }
    public virtual IList<Product> Products { get; set; }
}

public class ProductStock
{
    public virtual int Id { get; private set; }
    public virtual Product Product { get; set; }
    public virtual string WarehouseName { get; set; }
    public virtual int Stock { get; set; }
}   

现在，如果您编写以下条件来内部连接这些实体

var criteria = DetachedCriteria.For<Product>()
                .CreateCriteria("Category", JoinType.InnerJoin)
                .CreateCriteria("ProductStocks", "ps", JoinType.InnerJoin)
                .Add(Restrictions.Le("ps.Stock",10));

上面的条件不起作用，因为当第一个CreateCriteria运行时，它返回"Category“实体，因此当第二个CreateCriteria执行时，它不会在"Category”实体中找到属性ProductStocks，查询将失败。

因此，编写此标准的正确方法是

var criteria = DetachedCriteria.For<Product>()
                .CreateAlias("Category", "c", JoinType.InnerJoin)
                .CreateCriteria("ProductStocks", "ps", JoinType.InnerJoin)
                .Add(Restrictions.Le("ps.Stock",10));

当第一个CreateAlias运行时，它返回“产品”实体，当第二个CreateCriteria执行时，它将在“产品”实体中找到属性ProductStocks。

因此，TSQL将是这样的。

SELECT this_.ProductID     as ProductID8_2_,
       this_.Name          as Name8_2_,
       this_.Price         as Price8_2_,
       this_.CategoryID    as CategoryID8_2_,
       ps2_.ProductStockID as ProductS1_9_0_,
       ps2_.Stock          as Stock9_0_,
       ps2_.ProductID      as ProductID9_0_,
       ps2_.WarehouseID    as Warehous4_9_0_,
       c1_.CategoryID      as CategoryID0_1_,
       c1_.Name            as Name0_1_
FROM   [Product] this_
       inner join [ProductStock] ps2_ on this_.ProductID = ps2_.ProductID
       inner join [Category] c1_ on this_.CategoryID = c1_.CategoryID
WHERE  ps2_.Stock <= 10 

我希望这能有所帮助。

Answer 3

createAlias()原样返回原始条件结果createCriteria()返回使用createCriteria构造的新条件

不同之处在于链接方法时，例如

cr.createAlias().add(Restrictions.ilike("code"，"abc"))将对实体cr.createCriteria(" parent "，“p”)添加限制，.add(Restrictions.ilike(“Restrictions.ilike”，"abc"))将对其父实体添加限制