表达式树的子集合List <string> .Any
我正在建立使用表达式树的通用linq查询。 我在创建子集合表达式时遇到困难。 方法调用由于不兼容的类型而爆炸。 通常我知道该放什么，但Any（）方法调用让我感到困惑。 我尝试了所有我能想到的类型，但没有运气。 任何帮助，将不胜感激。
这是我的实体类：
public class Story : Entity
{
public string Author { get; set; }
public IList<string> Contributors { get; set; }
}
查询我想要生成表达式树：
var stories = new List<Story>();
stories.Where(p => p.Author.Contains("Test") || p.Contributors.Any(c => c.Contains("Test")));
到目前为止我所拥有的东西
public interface IFilterCriteria
{
string PropertyToCompare { get; set; }
object ValueToCompare { get; set; }
FilterOperator FilterOperator { get; set; }
bool IsList { get; set; }
Expression Expression { get; set; }
}
public static IQueryable<T> Filter<T>(this IQueryable<T> query, IList<IFilterCriteria> filterCriterias, LogicalOperator logicalOperator = LogicalOperator.And)
{
if (filterCriterias != null && filterCriterias.Any())
{
var resultCondition = filterCriterias.ToExpression(query, logicalOperator);
var parameter = Expression.Parameter(query.ElementType, "p");
if (resultCondition != null)
{
var lambda = Expression.Lambda(resultCondition, parameter);
var mce = Expression.Call(
typeof(Queryable), "Where",
new[] { query.ElementType },
query.Expression,
lambda);
return query.Provider.CreateQuery<T>(mce);
}
}
return query;
}
public static Expression ToExpression<T>(this IList<IFilterCriteria> filterCriterias, IQueryable<T> query, LogicalOperator logicalOperator = LogicalOperator.And)
{
Expression resultCondition = null;
if (filterCriterias.Any())
{
var parameter = Expression.Parameter(query.ElementType, "p");
foreach (var filterCriteria in filterCriterias)
{
var propertyExpression = filterCriteria.PropertyToCompare.Split('.').Aggregate<string, MemberExpression>(null, (current, property) => Expression.Property(current ?? (parameter as Expression), property));
Expression valueExpression;
var constantExpression = Expression.Constant(filterCriteria.ValueToCompare);
if (!filterCriteria.IsList)
{
valueExpression = Expression.Convert(constantExpression, propertyExpression.Type);
}
else
{
valueExpression = Expression.Call(typeof (Enumerable), "Any", new[] {typeof (string)},
propertyExpression, filterCriteria.Expression,
Expression.Constant(filterCriteria.ValueToCompare,
typeof (string)));
}
Expression condition;
switch (filterCriteria.FilterOperator)
{
case FilterOperator.IsEqualTo:
condition = Expression.Equal(propertyExpression, valueExpression);
break;
case FilterOperator.IsNotEqualTo:
condition = Expression.NotEqual(propertyExpression, valueExpression);
break;
case FilterOperator.IsGreaterThan:
condition = Expression.GreaterThan(propertyExpression, valueExpression);
break;
case FilterOperator.IsGreaterThanOrEqualTo:
condition = Expression.GreaterThanOrEqual(propertyExpression, valueExpression);
break;
case FilterOperator.IsLessThan:
condition = Expression.LessThan(propertyExpression, valueExpression);
break;
case FilterOperator.IsLessThanOrEqualTo:
condition = Expression.LessThanOrEqual(propertyExpression, valueExpression);
break;
case FilterOperator.Contains:
condition = Expression.Call(propertyExpression, typeof(string).GetMethod("Contains", new[] { typeof(string) }), valueExpression);
break;
case FilterOperator.StartsWith:
condition = Expression.Call(propertyExpression, typeof(string).GetMethod("StartsWith", new[] { typeof(string) }), valueExpression);
break;
case FilterOperator.EndsWith:
condition = Expression.Call(propertyExpression, typeof(string).GetMethod("EndsWith", new[] { typeof(string) }), valueExpression);
break;
default:
condition = valueExpression;
break;
}
if (resultCondition != null)
{
switch (logicalOperator)
{
case LogicalOperator.And:
resultCondition = Expression.AndAlso(resultCondition, condition);
break;
case LogicalOperator.Or:
resultCondition = Expression.OrElse(resultCondition, condition);
break;
}
}
else
{
resultCondition = condition;
}
}
}
return resultCondition;
}
这就是我使用表达式的方式：
var stories = new List<Story>();
var filters = new List<FilterCriteria>();
filter.Add(new FilterCriteria { ValueToCompare = "Test", PropertyToCompare = "Author", FilterOperator = FilterOperator.Contains });
Expression<Func<string, bool>> func = t => t.Contains("Test");
filter.Add(new FilterCriteria { ValueToCompare = "Test", PropertyToCompare = "Contributors", FilterOperator = FilterOperator.Contains, Expression = func });
stories.Filter(filters, LogicalOperator.Or).ToList();
但是在运行这段代码之后，我得到了这个我无法解决的错误
'System.Linq.Queryable'类型的泛型方法'Any'与提供的类型参数和参数兼容。 如果方法是非泛型的，则不应提供类型参数。 说明：执行当前Web请求期间发生未处理的异常。 请查看堆栈跟踪以获取有关该错误的更多信息以及源代码的位置。
异常详细信息：System.InvalidOperationException：类型'System.Linq.Queryable'中的泛型方法'Any'与提供的类型参数和参数兼容。 如果方法是非泛型的，则不应提供类型参数。
源错误：
184行：{185行：
var overload = typeof（Queryable）.GetMethods（）。Single（mi => mi.Name ==“Any”&& mi.GetParameters（）。Count（）== 2）; 186线：
Expression.Call（typeof（Queryable），“Any”，new [] {typeof（string）}，propertyExpression或）; 187行：
valueExpression = Expression.Call（typeof（Enumerable），“Any”，new [] {typeof（string）}，propertyExpression或Expression.Constant（“Test”，
您不要在代码中的Any位置调用Any方法。
您应该扩展Contains ，例如：
case FilterOperator.Contains:
// if collection
if (propertyExpression.Type.IsGenericType &&
typeof(IEnumerable<>)
.MakeGenericType(propertyExpression.Type.GetGenericArguments())
.IsAssignableFrom(propertyExpression.Type))
{
// find AsQueryable method
var toQueryable = typeof(Queryable).GetMethods()
.Where(m => m.Name == "AsQueryable")
.Single(m => m.IsGenericMethod)
.MakeGenericMethod(typeof(string));
// find Any method
var method = typeof(Queryable).GetMethods()
.Where(m => m.Name == "Any")
.Single(m => m.GetParameters().Length == 2)
.MakeGenericMethod(typeof(string));
// make expression
condition = Expression.Call(
null,
method,
Expression.Call(null, toQueryable, propertyExpression),
filterCriteria.Expression
);
}
else
{
condition = Expression.Call(propertyExpression, typeof(string).GetMethod("Contains", new[] { typeof(string) }), valueExpression);
}
break;
你也应该创建一个p参数（ Expression.Parameter(query.ElementType, "p") ），否则你会得到variable 'p' of type 'WpfApplication2.Story' referenced from scope '', but it is not defined错误。
您可以将parameter从Filter方法传递给ToExpression方法。