IQueryable IQueryProvider.CreateQuery(Expression expression)
{
var elementType = ExpressionUtility.ElementType(expression);
var queryable = CreateQuery(expression, elementType);
return(queryable);
}
protected override Expression VisitMethodCall(MethodCallExpression m)
{
var anonymousType = typeof(DataRow);
if (m.Method.Name == "Cast")
{
var castSourceType = ExpressionUtility.ElementType(m.Arguments[0]);
var castTargetType = ExpressionUtility.ElementType(m);
if (castTargetType.IsAssignableFrom(anonymousType))
{
this.typePaires.Add(castSourceType, castTargetType);
}
}
return(base.VisitMethodCall(m));
}
TResult IQueryProvider.Execute <TResult>(Expression expression)
{
expression = UpdateExpression(expression);
var isSingleValue = !typeof(IEnumerable).IsAssignableFrom(expression.Type) || expression.Type == typeof(string);
if (isSingleValue)
{
var obj = this.source.Execute <TResult>(expression);
return(obj);
}
var castSourceType = ExpressionUtility.ElementType(expression);
var castTargetType = GetElementType(typeof(TResult));
if (castSourceType != castTargetType)
{
expression = Expression.Call(typeof(Queryable), "Cast", new[] { castTargetType }, expression);
}
var items = this.source.Execute <TResult>(expression);
return(items);
}
protected override Expression VisitMethodCall(MethodCallExpression m)
{
//==============================================================
// 说明：将索引器字段转换为类的属性或字段
if (m.Method.Name == "get_Item" && m.Object != null && m.Object.Type == this.oldType)
{
Debug.Assert(m.Arguments.Count == 1);
var arg = m.Arguments[0];
Debug.Assert(arg.NodeType == ExpressionType.Constant);
Debug.Assert(arg.Type == typeof(string));
var name = (string)((ConstantExpression)arg).Value;
var pf = TypeUtility.FindPropertyOrField(this.newType, name, false);
if (pf == null)
{
throw Error.NoPublicPropertyOrField(name, newType);
}
Expression expr = Expression.MakeMemberAccess(this.parameter, pf);
if (m.Type != expr.Type)
{
expr = Expression.Convert(expr, m.Type);
}
return(expr);
}
//==============================================================
//==============================================================
// 说明：如果序列的实际类型与 Cast 的目标类型一致，则直接返回序列，而不进行转换。
// 例如：
// var q = db.CreateQuery("select p from Products as p").Cast<Product>();
// 由于序列的实际类型即是Product，因为，Cast 是多余的，直接除。即变为：
// db.CreateQuery("select p from Products as p")
//--------------------------------------------------------------
if (m.Method.Name == "Cast")
{
var castSourceType = ExpressionUtility.ElementType(m.Arguments[0]);
var castTargetType = ExpressionUtility.ElementType(m);
if (this.newType == castSourceType && this.oldType == castTargetType)
{
return(m.Arguments[0]);
}
}
//==============================================================
Expression instance = Visit(m.Object);
IEnumerable <Expression> arguments = VisitExpressionList(m.Arguments);
if ((instance == m.Object) && (arguments == m.Arguments))
{
return(m);
}
//==============================================================
// 说明：替换掉原来的类型
// 例如：
// var q = db.CreateQuery<IDataRecord>("select p from Products as p")
// 变为
// q = db.CreateQuery<Product>()
if (m.Method.IsGenericMethod)
{
var argTypes = m.Method.GetGenericArguments();
if (argTypes[0] == oldType)
{
var methodName = m.Method.Name;
var declareType = m.Method.DeclaringType;
argTypes[0] = newType;
var expr = Expression.Call(declareType, methodName, argTypes, arguments.ToArray());
return(expr);
}
}
//==============================================================
return(Expression.Call(instance, m.Method, arguments));
}
