我在NHibernate中使用JoinAlias QueryOver获得了一些意想不到的行为。
我的实体基本上是这样的:
public class Field
{
public virtual long Id { get; protected set; }
public virtual Field Parent { get; protected set; }
public virtual FieldType Type { get; protected set; }
public virtual string Value { get; protected set; }
...(Ctors etc
}
我的映射是这样的:
public class FieldMap : ClassMap<Field>
{
public FieldMap()
{
Id(x => x.Id)
.GeneratedBy.Native();
References(x => x.Type)
.Column("FieldTypeId")
.LazyLoad()
.Cascade.All()
;
Map(x => x.Value);
References(x => x.Parent)
.Column("ParentFieldId")
.Nullable()
.LazyLoad()
.Cascade.All()
;
}
我的查询:
Field fieldAlias = null;
string typeAlias = null;
Field parentFieldAlias = null;
var query = getSession().QueryOver<Field>(() => fieldAlias)
.JoinAlias(() => fieldAlias.Type, () => typeAlias)
.Where(() => typeAlias.Name == type)
.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
.Where(() => (parentFieldAlias.Value == parentValue) || (parentFieldAlias == null))
;
就我而言,这应该给我一些像这样的SQL:
... WHERE(a.ParentFieldId == NULL)OR(a.ParentFieldId = c.FieldId AND c.Value = parentValue)
但我得到一个空引用异常。 (我假设当别名被解析并且Parent为空时)。
例外情况如下:
System.NullReferenceException occurred
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=NHibernate
StackTrace:
at NHibernate.Criterion.ConstantProjection..ctor(Object value)
at NHibernate.Criterion.Projections.Constant(Object obj)
at NHibernate.Impl.ExpressionProcessor.FindMemberProjection(Expression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(Expression left, Expression right, ExpressionType nodeType)
at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(BinaryExpression be)
at NHibernate.Impl.ExpressionProcessor.ProcessBinaryExpression(BinaryExpression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessOrExpression(BinaryExpression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessBinaryExpression(BinaryExpression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessLambdaExpression(LambdaExpression expression)
at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression`1 expression)
at NHibernate.Criterion.QueryOver`2.Add(Expression`1 expression)
at NHibernate.Criterion.QueryOver`2.Where(Expression`1 expression)
at NHibernate.Criterion.QueryOver`2.NHibernate.IQueryOver<TRoot,TSubType>.Where(Expression`1 expression)
at Ismoos.Director.FieldOptionsQuery.Execute(Service service, String type, String parentValue) in D:\Work\Ismoos\Ismoos\Director\Ismoos.Director\FieldOptionsQuery.cs:line 31
InnerException:
我尝试过几种不同的方式,包括:
.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
.Where(Restrictions.Or(Restrictions.On(() => fieldAlias.Parent).IsNotNull,
Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue))))
但这些都不起作用。
我有一个解决方法,省略查询中父字段值的限制,并在QueryOver返回后执行LINQ查询,如下所示:
Field fieldAlias = null;
string typeAlias = null;
Field parentFieldAlias = null;
var query = getSession().QueryOver<Field>(() => fieldAlias)
.JoinAlias(() => fieldAlias.Type, () => typeAlias)
.Where(() => typeAlias.Name == type)
;
var list = query
.List<Field>()
;
return list
.Where(x => (x.Parent == null) || (x.Parent.Value == parentValue))
.ToList();
但这不如在QueryOver中那样最佳。
有什么建议吗?
答案 0 :(得分:7)
有限制的第二个解决方案可以胜任。有两个问题。我们需要LEFT JOIN到Parent,我看到一个错误:IsNotNull
应该是IsNull
来正确评估OR
语句:
破解IsNotNull
(很可能是内连接)
.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
.Where
(
Restrictions.Or(
Restrictions.On(() => fieldAlias.Parent).IsNotNull, // here
Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue)))
)
使用OR
和LEFT JOIN工作IsNull
:
.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias
, NHibernate.SqlCommand.JoinType.LeftOuterJoin)) // left join for NULL
.Where
(
Restrictions.Or(
Restrictions.On(() => fieldAlias.Parent).IsNull, // this is what we need
Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue))
);
第一个解决方案的问题是,我们无法为浮动/虚拟对象评估null: parentFieldAlias
.Where(()=&gt;(parentFieldAlias.Value == parentValue)|| (parentFieldAlias == null));
我们需要检查所有者的财产:fieldAlias.Parent
答案 1 :(得分:1)
我有类似的问题和条件之间的额外括号
喜欢
.Where(() => (parentFieldAlias.Value == parentValue) || (parentFieldAlias == null));
让事情适合我。