动态地创建 func、IOrderedQueryable>
本文关键字:TEntity IOrderedQueryable IQueryable func 动态 创建 | 更新日期: 2023-09-27 18:33:02
我想从SortingItems
列表中动态创建Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>
。我的意思是我想创建以下表达式:
entity => entity.OrderBy(c => c.Id).ThenBy(c => c.Name).ThenByDescending(c => c.LastName)
以下是我的代码:
[DataContract]
public class SortingItem
{
[DataMember]
public string PropertySelectorString { get; set; }
[DataMember]
public SortingDirectionsEnum SortingDirections { get; set; }
}
[DataContract]
public enum SortingDirectionsEnum
{
[EnumMember]
Descending = 0,
[EnumMember]
Ascending = 1
}
public Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> GetSortingFunc<TEntity>()
{
_entityType = typeof(TEntity);
_parameterExpression = Expression.Parameter(_entityType, "entity");
_iQueryableParameterExpression = Expression.Parameter(typeof(IQueryable<TEntity>), "f");
MethodInfo orderByMethodInfo = null;
Expression resultExpression = null;
foreach (SortingItem sortingItem in SortingItems)
{
MemberExpression memberExpression = GetLeftSide(sortingItem.PropertySelectorString, _entityType, _parameterExpression); // I'm dead sure about working this line
switch (sortingItem.SortingDirections)
{
case SortingDirectionsEnum.Descending:
orderByMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "OrderBy" && method.GetParameters().Length == 2).MakeGenericMethod(_entityType, memberExpression.Type);
if (resultExpression != null)
orderByMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "ThenBy" && method.GetParameters().Length == 2).MakeGenericMethod(_entityType, memberExpression.Type);
break;
case SortingDirectionsEnum.Ascending:
orderByMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "OrderByDescending" && method.GetParameters().Length == 2).MakeGenericMethod(_entityType, memberExpression.Type);
if (resultExpression != null)
orderByMethodInfo = typeof(Queryable).GetMethods().First(method => method.Name == "ThenByDescending" && method.GetParameters().Length == 2).MakeGenericMethod(_entityType, memberExpression.Type);
break;
}
MethodCallExpression methodCallExpression;
if (resultExpression != null)
// Exception
// An unhandled exception of type 'System.ArgumentException' occurred in System.Core.dll
// Additional information: Incorrect number of arguments supplied for call to method 'System.Linq.IOrderedQueryable`1[ConsoleApplication1.User] ThenBy[User,Int32](System.Linq.IOrderedQueryable`1[ConsoleApplication1.User], System.Linq.Expressions.Expression`1[System.Func`2[ConsoleApplication1.User,System.Int32]])'
methodCallExpression = Expression.Call(orderByMethodInfo, _iQueryableParameterExpression, resultExpression, Expression.Lambda(memberExpression, _parameterExpression));
else
methodCallExpression = Expression.Call(orderByMethodInfo, _iQueryableParameterExpression, Expression.Lambda(memberExpression, _parameterExpression));
resultExpression = Expression.Lambda(methodCallExpression, _iQueryableParameterExpression);
}
Expression<Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>> lambdaExpression = Expression.Lambda<Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>>>(resultExpression, _parameterExpression);
return lambdaExpression.Compile();
}
可以单独创建{f.OrderBy(entity => entity.Id)}
或{f.ThenBy(entity => entity.Name)}
,但我在以下行出现异常
methodCallExpression = Expression.Call(orderByMethodInfo, _iQueryableParameterExpression, resultExpression, Expression.Lambda(memberExpression, _parameterExpression));
我应该如何使用Expression.Call
将{f.OrderBy(entity => entity.Id)}
与{f.ThenBy(entity => entity.Name)}
结合起来,...?
我建议你不要写这样的代码,因为它很难阅读。过去我不得不维护那些怪物。
如果您确实对该解决方案感兴趣,则可以下载 DynamicLINQ,然后查询将如下所示:
public string GetSortCriteria(this SortingItem item){
return string.Format("{0} {1}", item.PropertySelectorString,
item.SortingDirections == SortingDirectionsEnum.Descending ?
"DESC" : "ASC");
}
// later:
var mergedSortCriteria= string.Join(",",
SortingItems.Select(item => item.GetSortCriteria());
Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> myFunc =
source => source.OrderBy("id " + mergedSortCriteria);