NHibernate Issues之1255：联合主键(composite-id)

.Domain

这里定义一个Domain——CustomerValue，这个持久化类有两个属性：联合主键(composite-id)和Value。

我们使用联合主键，首先需要定义联合主键的类型，同时这个类必须重载Equals()和GetHashCode()方法，来实现组合的标识符等同性判断。 例如下面的CustomerValue持久化类，其联合主键类型为CustomerValueId，就是Customer持久化类与int类型的复合形式，在CustomerValueId类中重载了Equals()和GetHashCode()方法。

public class Customer { public virtual int Id { get; set; } public virtual string Name { get; set; } } public class CustomerValue { public virtual CustomerValueId Id { get; set; } public virtual decimal Value { get; set; } } public class CustomerValueId : IEquatable<CustomerValueId> { private int? _requestedHashCode; public Customer Customer { get; set; } public int CustomKey { get; set; } public bool Equals(CustomerValueId other) { if (ReferenceEquals(null, other)) { return false; } if (ReferenceEquals(this, other)) { return true; } return Equals(other.Customer, Customer) && other.CustomKey == CustomKey; } public override bool Equals(object obj) { if (ReferenceEquals(null, obj)) { return false; } if (ReferenceEquals(this, obj)) { return true; } if (obj.GetType() != typeof(CustomerValueId)) { return false; } return Equals((CustomerValueId)obj); } public override int GetHashCode() { if (!_requestedHashCode.HasValue) { unchecked { _requestedHashCode = ((Customer != null ? Customer.GetHashCode() : base.GetHashCode()) * 397) ^ CustomKey; } } return _requestedHashCode.Value; } }

2.Mapping

需要对两个Domain映射，这里注重理解下联合主键的映射，这里是把类的Customer属性和CustomerKey属性组合成为标识符属性。<key-many-to-one>节点用于映射子元素，一般都是Domain(多对一关系的)；<key-property>节点用于映射属性。在这里我需要在<key-many-to-one>节点中设置not-found attribute来避免在运行时抛出异常，就是设置not-found="ignore"。

<class name="Customer"> <id name="Id"> <generator class="hilo" /> </id> <property name="Name" /> </class> <class name="CustomerValue" > <composite-id name="Id" class="CustomerValueId"> <key-many-to-one name="Customer" column="CustomerId" not-found="ignore" /> <key-property name="CustomKey" /> </composite-id> <property name="Value" /> </class>

3.Test

做完了上面的步骤，测试一下，保存一个CustomerValue。查询验证下并删除。这个测试很简单，就不贴出SQL结果了。

using (var session = OpenSession()) { using (var tx = session.BeginTransaction()) { var customer = new Customer { Name = "李永京" }; session.Save(customer); var customerValue = new CustomerValue { Id = new CustomerValueId { Customer = customer, CustomKey = 20012 }, Value = 1255.0m }; session.Save(customerValue); tx.Commit(); } using (var tx = session.BeginTransaction()) { var customerValue = session.CreateQuery("from CustomerValue c where c.Value=:value") .SetDecimal("value", 1255.0m) .UniqueResult<CustomerValue>(); session.Delete(customerValue); session.Delete("from Customer"); tx.Commit(); }