目标是使用NHibernate和Linq做这样的事情:
Session.Query<MyClass>().Where(x => x.DateGreaterThen(DateTime.Now))
这个例子有点简化,但想法是在Where谓词中我想调用MyClass方法。所以MyClass看起来像:
public class MyClass
{
public static readonly Expression<Func<MyClass, DateTime, bool>> GreaterThenExpression =
(x, dt) => x.MyDateTimeProperty > dt.Date;
private static readonly Func<MyClass, DateTime, bool> GreaterThenFunc = GreaterThenExpression.Compile();
public Guid Id { get; set; }
public DateTime MyDateTimeProperty { get; set; }
public bool DateGreaterThen(DateTime dt)
{
return GreaterThenFunc(this, dt);
}
}
自定义生成器:
public class EntityMethodGenerator<T1, T2, TResult> : BaseHqlGeneratorForMethod
{
private Expression<Func<T1, T2, TResult>> _returnValueExpression;
public EntityMethodGenerator()
{
SupportedMethods = new[]
{
ReflectionHelper.GetMethodDefinition<MyClass>(myClass => myClass.DateGreaterThen(DateTime.Now))
};
}
public static void Register(ILinqToHqlGeneratorsRegistry registry, Expression<Action<T1>> method, Expression<Func<T1, T2, TResult>> returnValueExpression)
{
var generator = new EntityMethodGenerator<T1, T2, TResult> { _returnValueExpression = returnValueExpression };
registry.RegisterGenerator(ReflectionHelper.GetMethodDefinition(method), generator);
}
public override HqlTreeNode BuildHql(
MethodInfo method,
Expression targetObject,
ReadOnlyCollection<Expression> arguments,
HqlTreeBuilder treeBuilder,
IHqlExpressionVisitor visitor)
{
return visitor.Visit(_returnValueExpression);
}
}
最后自定义自定义生成器注册表:
public class OwnLinqToHqlGeneratorsRegistry : DefaultLinqToHqlGeneratorsRegistry
{
public OwnLinqToHqlGeneratorsRegistry()
{
EntityMethodGenerator<MyClass, DateTime, bool>.Register(this, (myClass) => myClass.DateGreaterThen(DateTime.Now), MyClass.GreaterThenExpression);
}
}
但这不起作用,我得到System.Data.SqlClient.SqlException : Invalid column name 'dt'.
我怀疑我的BuildHql方法没有正确实现,有任何帮助解决这个问题吗?
顺便说一句,我想在生成器中使用表达式,比如GreaterThenExpression
,而不是在BuildHql
方法中手动构建HqlTree
答案 0 :(得分:1)
GreaterThenExpression是一个lamba。在BuildHql()中,您还需要注意targetObject和参数,否则您只是在HQL树中插入 unapplied lambda的一些HQL转换。
您需要提取lambda的主体并将其参数替换为targetObject和arguments。然后你可以从中生成HQL。尝试使用Remotion.Linq.Parsing.ExpressionTreeVisitors.MultiReplacingExpressionTreeVisitor。
(旁注,它应该是GreaterThan,而不是GreaterThen。)