mysql - NHibernate 和 MySQL Nullable 对象必须有一个值

Question

我遇到了一个问题，希望得到一些关于从哪里开始的指导。让我先介绍一下场景。

我最近从 SQL Server 迁移到 MySQl 数据库，所有针对 SQL Server 通过的集成测试现在都失败了，因为迁移出现了以下异常:

NHibernate.Exceptions.GenericADOException : could not execute query
[ select post0_.Id as Id1_, post0_.CreatedAt as CreatedAt1_, post0_.Title as Title1_, post0_.Body as Body1_, post0_.CreatedBy as CreatedBy1_, post0_.ParentId as ParentId1_ from Posts post0_, Users user1_ where post0_.CreatedBy=user1_.Id and ((user1_.Username is null) and (? is null) or user1_.Username=?) and (post0_.ParentId is null) order by post0_.CreatedAt desc ]
  Name:p1 - Value:username1
[SQL: select post0_.Id as Id1_, post0_.CreatedAt as CreatedAt1_, post0_.Title as Title1_, post0_.Body as Body1_, post0_.CreatedBy as CreatedBy1_, post0_.ParentId as ParentId1_ from Posts post0_, Users user1_ where post0_.CreatedBy=user1_.Id and ((user1_.Username is null) and (? is null) or user1_.Username=?) and (post0_.ParentId is null) order by post0_.CreatedAt desc]
  ----> System.InvalidOperationException : Nullable object must have a value

.

我使用带有 POCO 模型和手工 SQL 的 NHibernate v3(使用 DBDeploy.NET 管理数据库版本控制)

有可能，而且最有可能的是，我在将架构创建 SQL 从 SQL Server 转换为 MySQL 时犯了一个错误，但令我困惑的是，即使查询结果没有记录，我也会收到此错误。

为什么 NHibernate 试图创建任何对象？我不明白它是如何工作的？

这是其中一个查询的示例。返回行时这会引发异常。根据设计，唯一返回 null 的列是 Post.ParentId 列。

return GetSession()
    .Query<Post>()
    .Where(p => p.CreatedBy.Username == username && p.Parent == null)
    .OrderByDescending(p => p.CreatedAt)
    .Take(count)
    .ToList();

map 文件和类没有更改，但已包含它们以供下面引用。

非常欢迎任何我应该关注的想法。

邮政 map

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="clubrd.service" namespace="clubrd.service">
  <class name="Post" table="Posts">
    <id name="Id">
      <generator class="guid.comb"/>
    </id>
    <property name="CreatedAt"/>
    <property name="Title" column="Title"/>
    <property name="Body"/>
    <many-to-one name="CreatedBy" column="CreatedBy"/>
    <many-to-one name="Parent" column="ParentId"/>
    <set name="Children">
      <key column="ParentId"/>
      <one-to-many class="Post"/>
    </set>
  </class>
</hibernate-mapping>

用户映射，此处引用为 Post.CreatedBy

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="clubrd.service" namespace="clubrd.service">
  <class name="User" table="Users">
    <id name="Id">
      <generator class="guid.comb"/>
    </id>
    <property name="Username" not-null="true"/>
    <property name="Email" not-null="true"/>
    <property name="PasswordHash"/>
    <property name="PasswordSalt"/>
    <one-to-one name="Profile" class="Profile" />
  </class>
</hibernate-mapping>

Post 类

public class Post : Entity
{
    public virtual string Title { get; set; }
    public virtual string Body { get; set; }
    public virtual Post Parent { get; set; }
    public virtual ICollection<Post> Children { get; set; }
}

用户类

public class User : Entity
{
    public virtual string Name { get { return this.Username; } }
    public virtual string Username { get; set; }
    public virtual string PasswordHash { get; set; }
    public virtual string PasswordSalt { get; set; }
    public virtual string Email { get; set; }

    public virtual Profile Profile { get; set; }
    public virtual ICollection<ObjectRole> Roles { get; set; }
}

编辑错误点的完整输出以及前面显示正在构造的实体的 NHibernate 日志。

NHibernate.Cfg.SettingsFactory:  2010-12-18 15:56:20,159 INFO Default entity-mode: Poco
NHibernate.Cfg.SettingsFactory:  2010-12-18 15:56:20,160 INFO Named query checking : enabled
NHibernate.Impl.SessionFactoryImpl:  2010-12-18 15:56:20,211 INFO building session factory
NHibernate.Impl.SessionFactoryObjectFactory:  2010-12-18 15:56:20,580 INFO no name configured
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,389 INFO handling property dereference [clubrd.service.Post (p) -> CreatedBy (Class)]
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,406 INFO handling property dereference [clubrd.service.User () -> Username (Class)]
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,416 INFO handling property dereference [clubrd.service.Post (p) -> CreatedBy (Class)]
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,417 INFO handling property dereference [clubrd.service.User () -> Username (Class)]
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,419 INFO handling property dereference [clubrd.service.Post (p) -> Parent (Class)]
NHibernate.Hql.Ast.ANTLR.Tree.FromElement:  2010-12-18 15:56:21,424 INFO handling property dereference [clubrd.service.Post (p) -> CreatedAt (Class)]
NHibernate.Util.ADOExceptionReporter:  2010-12-18 15:56:21,564 WARN System.InvalidOperationException: Nullable object must have a value.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
   at System.Nullable`1.get_Value()
   at NHibernate.Dialect.MySQLDialect.GetLimitString(SqlString querySqlString, Int32 offset, Int32 limit, Nullable`1 offsetParameterIndex, Nullable`1 limitParameterIndex) in d:\CSharp\NH\nhibernate\src\NHibernate\Dialect\MySQLDialect.cs:line 197
   at NHibernate.Loader.Loader.PrepareQueryCommand(QueryParameters queryParameters, Boolean scroll, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1119
   at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 399
   at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 236
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1665
NHibernate.Util.ADOExceptionReporter:  2010-12-18 15:56:21,576 ERROR Nullable object must have a value.
NHibernate.Util.ADOExceptionReporter:  2010-12-18 15:56:21,577 WARN System.InvalidOperationException: Nullable object must have a value.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
   at System.Nullable`1.get_Value()
   at NHibernate.Dialect.MySQLDialect.GetLimitString(SqlString querySqlString, Int32 offset, Int32 limit, Nullable`1 offsetParameterIndex, Nullable`1 limitParameterIndex) in d:\CSharp\NH\nhibernate\src\NHibernate\Dialect\MySQLDialect.cs:line 197
   at NHibernate.Loader.Loader.PrepareQueryCommand(QueryParameters queryParameters, Boolean scroll, ISessionImplementor session) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1119
   at NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 399
   at NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 236
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs:line 1665
NHibernate.Util.ADOExceptionReporter:  2010-12-18 15:56:21,579 ERROR Nullable object must have a value.

NHibernate.Exceptions.GenericADOException : could not execute query
[ select post0_.Id as Id1_, post0_.CreatedAt as CreatedAt1_, post0_.Title as Title1_, post0_.Body as Body1_, post0_.CreatedBy as CreatedBy1_, post0_.ParentId as ParentId1_ from Posts post0_, Users user1_ where post0_.CreatedBy=user1_.Id and ((user1_.Username is null) and (? is null) or user1_.Username=?) and (post0_.ParentId is null) order by post0_.CreatedAt desc ]
  Name:p1 - Value:username1
[SQL: select post0_.Id as Id1_, post0_.CreatedAt as CreatedAt1_, post0_.Title as Title1_, post0_.Body as Body1_, post0_.CreatedBy as CreatedBy1_, post0_.ParentId as ParentId1_ from Posts post0_, Users user1_ where post0_.CreatedBy=user1_.Id and ((user1_.Username is null) and (? is null) or user1_.Username=?) and (post0_.ParentId is null) order by post0_.CreatedAt desc]
  ----> System.InvalidOperationException : Nullable object must have a value.
at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1674
at NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1589
at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet`1 querySpaces, IType[] resultTypes) in d:\CSharp\NH\nhibernate\src\NHibernate\Loader\Loader.cs: line 1583
at NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\Loader\QueryLoader.cs: line 298
at NHibernate.Hql.Ast.ANTLR.QueryTranslatorImpl.List(ISessionImplementor session, QueryParameters queryParameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Hql\Ast\ANTLR\QueryTranslatorImpl.cs: line 110
at NHibernate.Engine.Query.HQLQueryPlan.PerformList(QueryParameters queryParameters, ISessionImplementor session, IList results) in d:\CSharp\NH\nhibernate\src\NHibernate\Engine\Query\HQLQueryPlan.cs: line 105
at NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters queryParameters, IList results) in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs: line 658
at NHibernate.Impl.SessionImpl.List(IQueryExpression queryExpression, QueryParameters parameters) in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs: line 634
at NHibernate.Impl.ExpressionQueryImpl.List() in d:\CSharp\NH\nhibernate\src\NHibernate\Impl\ExpressionQueryImpl.cs: line 63
at NHibernate.Linq.NhQueryProvider.ExecuteQuery(NhLinqExpression nhLinqExpression, IQuery query, NhLinqExpression nhQuery) in d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs: line 78
at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) in d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs: line 27
at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) in d:\CSharp\NH\nhibernate\src\NHibernate\Linq\NhQueryProvider.cs: line 102
at Remotion.Data.Linq.QueryableBase`1.GetEnumerator()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList(IEnumerable`1 source)
at clubrd.data.Repository.PostRepository.UsersLatestPosts(String username, Int32 count) in PostRepository.cs: line 13
at clubrd.data.integrationtest.Repository.PostRepositoryTests.UsersPosts() in PostRepositoryTests.cs: line 103
--InvalidOperationException

Answer 1

感谢 Mauricio 为我指明了堆栈跟踪。这似乎是 MySQL5Dialect 的 GetLimitString() 实现的问题。将方言从 MySQL5Dialect 更改为 MySQLDialect 似乎可以解决该问题。

虽然，也许我累了，但是当我查看代码时，MySQL 版本似乎包含此异常的风险，而不是 MySQL5 版本。

MySQL方言

public override SqlString GetLimitString(SqlString querySqlString, int offset, int limit, int? offsetParameterIndex, int? limitParameterIndex)
        {
            var pagingBuilder = new SqlStringBuilder();
            pagingBuilder.Add(querySqlString);
            pagingBuilder.Add(" limit ");

            if (offset > 0)
            {
                pagingBuilder.Add(Parameter.WithIndex(offsetParameterIndex.Value));
                pagingBuilder.Add(", ");
            }

            pagingBuilder.Add(Parameter.WithIndex(limitParameterIndex.Value));

            return pagingBuilder.ToSqlString();
        }

MySQL5方言

public override SqlString GetLimitString(SqlString querySqlString, int offset, int limit)
        {
            var pagingBuilder = new SqlStringBuilder();

            pagingBuilder.Add(querySqlString);
            pagingBuilder.Add(" limit ");
            if (offset > 0)
            {
                pagingBuilder.Add(offset.ToString());
                pagingBuilder.Add(", ");
            }

            pagingBuilder.Add(limit.ToString());

            return pagingBuilder.ToSqlString();
        }