Question

我有以下Domain Model(s)：

public class WriteOffApprovalUser
{
    public virtual string UserName { get; set; }
    public virtual Employee Employee { get; set; }
}

public class Employee
{
    public virtual string EmployeeID { get; set; }
    public virtual string EmployeeStatusCode { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual string PreferredName { get; set; }
    public virtual string JobTitle { get; set; }
    public virtual string Division { get; set; }
    public virtual string Department { get; set; }
    public virtual string Location { get; set; }
    public virtual string City { get; set; }
    public virtual string DeskLocation { get; set; }
    public virtual string MailID { get; set; }
    public virtual string Phone { get; set; }
    public virtual string Fax { get; set; }
    public virtual string SecCode { get; set; }
    public virtual string UserId { get; set; }
    public virtual string SupervisorID { get; set; }
}

这些是我的Fluent Mappings

public class WriteOffApprovalUserMap : ClassMap<WriteOffApprovalUser>
{
    public WriteOffApprovalUserMap()
    {
        //Schema("LEGAL");
        Table("WRITEOFF_APPROVAL_USER");

        Id(x => x.UserName).Column("USER_NAME");

        HasOne(x => x.Employee).PropertyRef("UserId");

    }
}

public class EmployeeMap : ClassMap<Employee>
{
    public EmployeeMap()
    {
        // Table Name
        //Schema("ADP_FEED_OWNER");
        Table("ADP_EMPLOYEE");

        // Primary Key
        Id(x => x.EmployeeID).Column("EMPLID");

        // Mappings
        Map(x => x.UserId).Column("USER_ID");
        Map(x => x.FirstName).Column("FIRST_NAME");
        Map(x => x.LastName).Column("LAST_NAME");
        Map(x => x.PreferredName).Column("PREFERRED_NAME");
    }
}

这是我的查询：

var results = new Repository<WriteOffApprovalUser>(session)
                    .Query()
                    .ToList();

这是它正在生成的SQL，而我正期待一个JOIN。

select writeoffap0_.USER_NAME as USER1_1_ from WRITEOFF_APPROVAL_USER writeoffap0_
SELECT employee0_.EMPLID as EMPLID0_0_, employee0_.USER_ID as USER2_0_0_, employee0_.FIRST_NAME as FIRST3_0_0_, employee0_.LAST_NAME as LAST4_0_0_, employee0_.PREFERRED_NAME as PREFERRED5_0_0_ FROM ADP_EMPLOYEE employee0_ WHERE employee0_.EMPLID=:p0;
SELECT employee0_.EMPLID as EMPLID0_0_, employee0_.USER_ID as USER2_0_0_, employee0_.FIRST_NAME as FIRST3_0_0_, employee0_.LAST_NAME as LAST4_0_0_, employee0_.PREFERRED_NAME as PREFERRED5_0_0_ FROM ADP_EMPLOYEE employee0_ WHERE employee0_.EMPLID=:p0;
SELECT employee0_.EMPLID as EMPLID0_0_, employee0_.USER_ID as USER2_0_0_, employee0_.FIRST_NAME as FIRST3_0_0_, employee0_.LAST_NAME as LAST4_0_0_, employee0_.PREFERRED_NAME as PREFERRED5_0_0_ FROM ADP_EMPLOYEE employee0_ WHERE employee0_.EMPLID=:p0;
SELECT employee0_.EMPLID as EMPLID0_0_, employee0_.USER_ID as USER2_0_0_, employee0_.FIRST_NAME as FIRST3_0_0_, employee0_.LAST_NAME as LAST4_0_0_, employee0_.PREFERRED_NAME as PREFERRED5_0_0_ FROM ADP_EMPLOYEE employee0_ WHERE employee0_.EMPLID=:p0;

现在数据库中有四行，正确的数据会回来，但我不希望有五个单独的SQL语句来执行此操作。

Answer 1

您需要急切地加载/获取Employee实体，以避免您看到的行为，这通常被称为SELECT N + 1问题。为此，您有两种选择：

选项1。在映射中急切加载意味着当您查询WriteOffApprovalUser实体时，它将始终执行对Employee表的JOIN。注意：这可能听起来像你想要的但是要小心，因为你会强迫所有使用这个实体的开发人员坚持这个设计决定，直到时间结束。您将不得不问自己，我是否想要查询WriteOffApprovalUser表并且不对Employee表执行JOIN。如果答案是肯定的，那么请不要在映射文件中强制加载。

要自动获取Employee，请将映射中的HasOne代码更改为如下所示：

HasOne(x => x.Employee).PropertyRef("UserId").Not.LazyLoad().Fetch.Join();

选项2。在查询中执行预先加载。我注意到你正在使用某种T模式的存储库，所以你可能需要修改它以处理急切的加载。使用NHibernate.Linq命名空间中的LINQ Query<T>类内置的NHibernate进行的典型热切加载看起来像这样：

var results = new session.Query<WriteOffApprovalUser>()
                    .Fetch( x => x.Employee ) // This will tell NHibernate to perform a JOIN to the Employee table
                    .ToList();

NHibernate一对一的关系

1 个答案: