我正在尝试使用表达式访问者修改 MemberBinding 表达式。但是当我尝试编译修改后的表达式时出现错误:
从范围''引用'EFTest.Views.TestView'类型的'变量'源',但未定义'
我还想提一下,如果我在 VisitMemberBinding 函数中返回 MemberBinding,我不会收到任何错误。我还确保修改后的表达式与原始表达式完全相同。
这项工作的最终目的是阻止 EntityFramework Core 中所有 linq 查询中的特定列。如果您对此有任何建议,请告诉我。
示例代码如下
class Expre
{
static void Main(string[] args)
{
DataContext context = new DataContext();
var rs = context.Query<TestView>().Select(m => new MyModel()
{
Id = m.DocumentId,
});
Visitor visitor = new Visitor();
var ss = visitor.Modify(rs.Expression);
var CompiledLambdaExpression = Expression.Lambda(ss).Compile();
EntityQueryable<MyModel> queryAble = (EntityQueryable<MyModel>)CompiledLambdaExpression.DynamicInvoke();
var rss = Enumerable.ToList(queryAble);
}
}
public class Visitor : ExpressionVisitor
{
public MemberBinding MemberBinding;
public Expression Modify(Expression expression)
{
var r = Visit(expression);
return r;
}
protected override MemberBinding VisitMemberBinding(MemberBinding node)
{
Type targetType = typeof(MyModel);
Type sourceType = typeof(TestView);
PropertyInfo SourceProperty = sourceType.GetProperty("DocumentId");
PropertyInfo TargetProperty = targetType.GetProperty("Id");
ParameterExpression parameterExpression = Expression.Parameter(sourceType, "m");
MemberExpression propertyExpression = Expression.Property(parameterExpression, SourceProperty);
MemberBinding memberBinding = Expression.Bind(TargetProperty, propertyExpression);
return base.VisitMemberBinding(memberBinding);
}
protected override Expression VisitParameter(ParameterExpression node)
{
return base.VisitParameter(node);
}
}
public class MyModel
{
public Int32 Id { get; set; }
public string Name { get; set; }
}
public class TestView
{
public Int32 Code { get; set; }
public string LanguageCode { get; set; }
public Int32 DocumentId { get; set; }
}