C# 如何在执行之前包装实体框架以截获LINQ表达式?
我想在执行之前重写LINQ表达式的某些部分。我在将重写器注入正确的位置时遇到了问题(事实上) 查看实体框架源代码(在reflector中),它最终归结为C# 如何在执行之前包装实体框架以截获LINQ表达式?,c#,linq,entity-framework,expression-trees,C#,Linq,Entity Framework,Expression Trees,我想在执行之前重写LINQ表达式的某些部分。我在将重写器注入正确的位置时遇到了问题(事实上) 查看实体框架源代码(在reflector中),它最终归结为IQueryProvider.Execute,它在EF中通过ObjectContext提供内部IQueryProvider提供程序{get;}属性耦合到表达式 因此,我创建了一个包装类(实现IQueryProvider),在调用Execute时重写表达式,然后将其传递给原始提供程序 问题是,Provider后面的字段是private Object
IQueryProvider.Execute
,它在EF中通过ObjectContext
提供内部IQueryProvider提供程序{get;}
属性耦合到表达式
因此,我创建了一个包装类(实现IQueryProvider
),在调用Execute时重写表达式,然后将其传递给原始提供程序
问题是,Provider
后面的字段是private ObjectQueryProvider\u queryProvider代码>。此ObjectQueryProvider
是一个内部密封类,这意味着不可能创建提供添加重写的子类
由于ObjectContext的紧密耦合,这种方法使我陷入了死胡同
如何解决这个问题?我看错方向了吗?是否有一种方法可以将自己注入到这个ObjectQueryProvider
更新:当您使用存储库模式“包装”ObjectContext时,所提供的解决方案都可以工作,但最好使用允许直接使用ObjectContext生成的子类的解决方案。从而与动态数据脚手架保持兼容 我有您需要的源代码,但不知道如何附加文件
以下是一些代码片段(代码片段!我不得不修改这段代码,所以它可能无法编译):
IQueryable:
public class QueryTranslator<T> : IOrderedQueryable<T>
{
private Expression _expression = null;
private QueryTranslatorProvider<T> _provider = null;
public QueryTranslator(IQueryable source)
{
_expression = Expression.Constant(this);
_provider = new QueryTranslatorProvider<T>(source);
}
public QueryTranslator(IQueryable source, Expression e)
{
if (e == null) throw new ArgumentNullException("e");
_expression = e;
_provider = new QueryTranslatorProvider<T>(source);
}
public IEnumerator<T> GetEnumerator()
{
return ((IEnumerable<T>)_provider.ExecuteEnumerable(this._expression)).GetEnumerator();
}
IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return _provider.ExecuteEnumerable(this._expression).GetEnumerator();
}
public Type ElementType
{
get { return typeof(T); }
}
public Expression Expression
{
get { return _expression; }
}
public IQueryProvider Provider
{
get { return _provider; }
}
}
公共类查询Translator:IOrderedQueryable
{
私有表达式_Expression=null;
私有查询TranslatorProvider _provider=null;
公共查询Translator(iQueryTable源)
{
_表达式=表达式常数(this);
_provider=新的QueryTranslatorProvider(源);
}
公共查询Translator(IQueryable源,表达式e)
{
如果(e==null)抛出新的ArgumentNullException(“e”);
_表达式=e;
_provider=新的QueryTranslatorProvider(源);
}
公共IEnumerator GetEnumerator()
{
return((IEnumerable)_provider.executenumerable(this._表达式)).GetEnumerator();
}
IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
返回_provider.executenumerable(this._表达式).GetEnumerator();
}
公共类型ElementType
{
获取{return typeof(T);}
}
公开表达
{
获取{return\u expression;}
}
公共IQueryProvider提供程序
{
获取{return\u provider;}
}
}
IQueryProvider:
public class QueryTranslatorProvider<T> : ExpressionTreeTranslator, IQueryProvider
{
IQueryable _source;
public QueryTranslatorProvider(IQueryable source)
{
if (source == null) throw new ArgumentNullException("source");
_source = source;
}
#region IQueryProvider Members
public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
return new QueryTranslator<TElement>(_source, expression) as IQueryable<TElement>;
}
public IQueryable CreateQuery(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Type elementType = expression.Type.FindElementTypes().First();
IQueryable result = (IQueryable)Activator.CreateInstance(typeof(QueryTranslator<>).MakeGenericType(elementType),
new object[] { _source, expression });
return result;
}
public TResult Execute<TResult>(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
object result = (this as IQueryProvider).Execute(expression);
return (TResult)result;
}
public object Execute(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Expression translated = this.Visit(expression);
return _source.Provider.Execute(translated);
}
internal IEnumerable ExecuteEnumerable(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Expression translated = this.Visit(expression);
return _source.Provider.CreateQuery(translated);
}
#endregion
#region Visits
protected override MethodCallExpression VisitMethodCall(MethodCallExpression m)
{
return m;
}
protected override Expression VisitUnary(UnaryExpression u)
{
return Expression.MakeUnary(u.NodeType, base.Visit(u.Operand), u.Type.ToImplementationType(), u.Method);
}
#endregion
}
公共类QueryTranslator提供程序:ExpressionTreeTranslator,IQueryProvider
{
IQueryable_源;
公共查询Translator提供程序(iQueryTable源)
{
如果(source==null)抛出新的ArgumentNullException(“source”);
_来源=来源;
}
#区域提供程序成员
公共IQueryable CreateQuery(表达式)
{
如果(表达式==null)抛出新的ArgumentNullException(“表达式”);
将新的QueryTranslator(_source,expression)返回为IQueryable;
}
公共IQueryable CreateQuery(表达式)
{
如果(表达式==null)抛出新的ArgumentNullException(“表达式”);
Type elementType=expression.Type.FindElementTypes().First();
IQueryable结果=(IQueryable)Activator.CreateInstance(typeof(QueryTranslator).MakeGenericType(elementType),
新对象[]{u源,表达式});
返回结果;
}
公共TResult执行(表达式)
{
如果(表达式==null)抛出新的ArgumentNullException(“表达式”);
对象结果=(作为IQueryProvider)。执行(表达式);
返回(TResult)结果;
}
公共对象执行(表达式)
{
如果(表达式==null)抛出新的ArgumentNullException(“表达式”);
Expression translated=this.Visit(Expression);
返回_source.Provider.Execute(已翻译);
}
内部IEnumerable可执行IEnumerable(表达式)
{
如果(表达式==null)抛出新的ArgumentNullException(“表达式”);
Expression translated=this.Visit(Expression);
返回_source.Provider.CreateQuery(已翻译);
}
#端区
#地区访问
受保护的重写MethodCallExpression VisitMethodCall(MethodCallExpression m)
{
返回m;
}
受保护的重写表达式VisitUnary(UnaryU表达式)
{
返回表达式.MakeUnary(u.NodeType,base.Visite(u.Operator),u.Type.ToImplementationType(),u.Method);
}
#端区
}
用法(警告:改编代码!可能无法编译):
private Dictionary\u table=new Dictionary();
公共覆盖IQueryable GetObjectQuery()
{
if(!\u表格容器(类型))
{
_表[type]=新的查询Translator(
_ctx.CreateQuery(“[”+typeof(T.Name+“]”);
}
返回(IQueryable)\表[类型];
}
表达访客/翻译:
编辑:添加了FindElementTypes()。希望所有的方法现在都存在
/// <summary>
/// Finds all implemented IEnumerables of the given Type
/// </summary>
public static IQueryable<Type> FindIEnumerables(this Type seqType)
{
if (seqType == null || seqType == typeof(object) || seqType == typeof(string))
return new Type[] { }.AsQueryable();
if (seqType.IsArray || seqType == typeof(IEnumerable))
return new Type[] { typeof(IEnumerable) }.AsQueryable();
if (seqType.IsGenericType && seqType.GetGenericArguments().Length == 1 && seqType.GetGenericTypeDefinition() == typeof(IEnumerable<>))
{
return new Type[] { seqType, typeof(IEnumerable) }.AsQueryable();
}
var result = new List<Type>();
foreach (var iface in (seqType.GetInterfaces() ?? new Type[] { }))
{
result.AddRange(FindIEnumerables(iface));
}
return FindIEnumerables(seqType.BaseType).Union(result);
}
/// <summary>
/// Finds all element types provided by a specified sequence type.
/// "Element types" are T for IEnumerable<T> and object for IEnumerable.
/// </summary>
public static IQueryable<Type> FindElementTypes(this Type seqType)
{
return seqType.FindIEnumerables().Select(t => t.IsGenericType ? t.GetGenericArguments().Single() : typeof(object));
}
//
///查找给定类型的所有已实现IEnumerable
///
公共静态IQueryable FindEnumerables(此类型为seqType)
{
if(seqType==null | | seqType==typeof(object)| | seqType==typeof(string))
返回新类型[]{}.AsQueryable();
if(seqType.IsArray | seqType==typeof(IEnumerable))
返回新类型[]{typeof(IEnumerable)}.AsQueryable();
if(seqType.IsGenericType&&seqType.GetGenericArguments().Length==1&&seqType.GetGenericTypeDefinition()==typeof(IEnumerable))
/// <summary>
/// Finds all implemented IEnumerables of the given Type
/// </summary>
public static IQueryable<Type> FindIEnumerables(this Type seqType)
{
if (seqType == null || seqType == typeof(object) || seqType == typeof(string))
return new Type[] { }.AsQueryable();
if (seqType.IsArray || seqType == typeof(IEnumerable))
return new Type[] { typeof(IEnumerable) }.AsQueryable();
if (seqType.IsGenericType && seqType.GetGenericArguments().Length == 1 && seqType.GetGenericTypeDefinition() == typeof(IEnumerable<>))
{
return new Type[] { seqType, typeof(IEnumerable) }.AsQueryable();
}
var result = new List<Type>();
foreach (var iface in (seqType.GetInterfaces() ?? new Type[] { }))
{
result.AddRange(FindIEnumerables(iface));
}
return FindIEnumerables(seqType.BaseType).Union(result);
}
/// <summary>
/// Finds all element types provided by a specified sequence type.
/// "Element types" are T for IEnumerable<T> and object for IEnumerable.
/// </summary>
public static IQueryable<Type> FindElementTypes(this Type seqType)
{
return seqType.FindIEnumerables().Select(t => t.IsGenericType ? t.GetGenericArguments().Single() : typeof(object));
}
public override IQueryable<T> GetObjectQuery<T>()
{
if (!_table.ContainsKey(type))
{
_table[type] = new QueryTranslator<T>(
_ctx.CreateObjectSet<T>();
}
return (IQueryable<T>)_table[type];
}
public override IQueryable<T> GetObjectQuery<T>()
{
if (!_table.ContainsKey(type))
{
_table[type] = new QueryTranslator<T>(
_ctx.CreateQuery<T>("[" + GetEntitySetName<T>() + "]"));
}
return (IQueryable<T>)_table[type];
}
public class QueryTranslator<T> : IOrderedQueryable<T>
{
private Expression expression = null;
private QueryTranslatorProvider<T> provider = null;
public QueryTranslator(IQueryable source)
{
expression = Expression.Constant(this);
provider = new QueryTranslatorProvider<T>(source);
}
public QueryTranslator(IQueryable source, Expression e)
{
if (e == null) throw new ArgumentNullException("e");
expression = e;
provider = new QueryTranslatorProvider<T>(source);
}
public IEnumerator<T> GetEnumerator()
{
return ((IEnumerable<T>)provider.ExecuteEnumerable(this.expression)).GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return provider.ExecuteEnumerable(this.expression).GetEnumerator();
}
public QueryTranslator<T> Include(String path)
{
ObjectQuery<T> possibleObjectQuery = provider.source as ObjectQuery<T>;
if (possibleObjectQuery != null)
{
return new QueryTranslator<T>(possibleObjectQuery.Include(path));
}
else
{
throw new InvalidOperationException("The Include should only happen at the beginning of a LINQ expression");
}
}
public Type ElementType
{
get { return typeof(T); }
}
public Expression Expression
{
get { return expression; }
}
public IQueryProvider Provider
{
get { return provider; }
}
}
public class QueryTranslatorProvider<T> : ExpressionVisitor, IQueryProvider
{
internal IQueryable source;
public QueryTranslatorProvider(IQueryable source)
{
if (source == null) throw new ArgumentNullException("source");
this.source = source;
}
public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
return new QueryTranslator<TElement>(source, expression) as IQueryable<TElement>;
}
public IQueryable CreateQuery(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Type elementType = expression.Type.GetGenericArguments().First();
IQueryable result = (IQueryable)Activator.CreateInstance(typeof(QueryTranslator<>).MakeGenericType(elementType),
new object[] { source, expression });
return result;
}
public TResult Execute<TResult>(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
object result = (this as IQueryProvider).Execute(expression);
return (TResult)result;
}
public object Execute(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Expression translated = this.Visit(expression);
return source.Provider.Execute(translated);
}
internal IEnumerable ExecuteEnumerable(Expression expression)
{
if (expression == null) throw new ArgumentNullException("expression");
Expression translated = this.Visit(expression);
return source.Provider.CreateQuery(translated);
}
#region Visitors
protected override Expression VisitConstant(ConstantExpression c)
{
// fix up the Expression tree to work with EF again
if (c.Type == typeof(QueryTranslator<T>))
{
return source.Expression;
}
else
{
return base.VisitConstant(c);
}
}
#endregion
}
public IQueryable<User> List()
{
return new QueryTranslator<User>(entities.Users).Include("Department");
}