private static Expression ChangeSource_VisitMethodCall(MethodCallExpression node, Dictionary <Type, Type> typeMap, Dictionary <string, ParameterExpression> paramters = null)
{
var theMethod = node;
var args = theMethod.Arguments.ToList();
for (int i = 0; i < args.Count; i++)
{
args[i] = new ArgumentVisitor(paramters ?? ChangeSource_BuildParamters(args[i], typeMap), typeMap).Visit(args[i]);
}
var genericArguments = theMethod.Method.GetGenericArguments().ToList();
for (int i = 0; i < genericArguments.Count; i++)
{
if (typeMap.ContainsKey(genericArguments[i]))
{
genericArguments[i] = typeMap[genericArguments[i]];
}
}
return(Expression.Call(
node.Method.DeclaringType,
node.Method.Name,
genericArguments.ToArray(),
args.ToArray()));
}
/// <summary>
/// 切换数据源,保留原数据源中的Expression
/// </summary>
/// <param name="source">原数据源</param>
/// <param name="targetSource">目标数据源</param>
/// <returns></returns>
public static IQueryable ChangeSource(this IQueryable source, IQueryable targetSource)
{
if (!(source is IQueryable && targetSource is IQueryable))
{
throw new Exception("仅支持EF的IQueryable!");
}
Dictionary <Type, Type> typeMap = new Dictionary <Type, Type>();
var oldQuery = source.GetObjQuery() as IQueryable;
var newQuery = targetSource.GetObjQuery() as IQueryable;
typeMap[oldQuery.ElementType] = newQuery.ElementType;
var methods = GetMethods(source.Expression);
Expression newExpression = newQuery.Expression;
Expression oldExpression = oldQuery.Expression;
while (true)
{
if (methods.Count == 0)
{
break;
}
var theMethod = methods.Pop();
string methodName = theMethod.Method.Name;
if (theMethod.Method.Name == "AsNoTracking")
{
continue;
}
var args = theMethod.Arguments.ToList();
args[0] = newExpression;
for (int i = 1; i < args.Count; i++)
{
args[i] = new ArgumentVisitor(ChangeSource_BuildParamters(args[i], typeMap), typeMap).Visit(args[i]);
}
var genericArguments = theMethod.Method.GetGenericArguments().ToList();
for (int i = 0; i < genericArguments.Count; i++)
{
if (typeMap.ContainsKey(genericArguments[i]))
{
genericArguments[i] = typeMap[genericArguments[i]];
}
}
newExpression = Expression.Call(
typeof(Queryable),
methodName,
genericArguments.ToArray(),
args.ToArray());
newQuery = newQuery.Provider.CreateQuery(newExpression);
oldExpression = Expression.Call(
typeof(Queryable),
methodName,
theMethod.Method.GetGenericArguments(),
theMethod.Arguments.ToArray());
oldQuery = oldQuery.Provider.CreateQuery(oldExpression);
typeMap[oldQuery.ElementType] = newQuery.ElementType;
}
return(targetSource.Provider.CreateQuery(newExpression));
Stack <MethodCallExpression> GetMethods(Expression expression)
{
Stack <MethodCallExpression> resList = new Stack <MethodCallExpression>();
Expression next = expression;
while (true)
{
if (next is MethodCallExpression methodCall)
{
resList.Push(methodCall);
next = methodCall.Arguments[0];
}
else
{
break;
}
}
return(resList);
}
}
