如何用表达式树表达 All have Any

Question

对于给定的搜索标签过滤器，预期结果是一个表达式，表示具有给定标签 ID 列表中所有标签的实体。

Lambda 可能表示为：

class Tag 
{
   public long TagId { get; set; }
}

class Taggable 
{
   ICollection<Tag> Tags { get; set; }
}

...

IEnumerable<long> searchTags = new List<long>() { 1, 2, 3 };
Func<Taggable, bool> filter = taggable => searchTags.All(qtag => taggable.Tags.Any(tag => tag.TagId == qtag));

将此表示为表达式树的尝试失败：

var tagParam = Expression.Parameter(typeof(Tag), "tag");    
var taggableParam = Expression.Parameter(typeof(Taggable), "taggable");
MemberExpression tagsProperty = Expression.Property(taggableParam, "Tags");
ConstantExpression searchTagsConstant = Expression.Constant(searchTags);

var containsCall = Expression.Call(
      typeof(Enumerable), "Contains",
      new[] { typeof(long) },
      searchTagsConstant,
      Expression.Property(tagParam, "TagID")
);

var anyCall = Expression.Call(
     typeof(Enumerable), "Any",
     new[] { typeof(Tag) },
     tagsProperty,
     Expression.Lambda(containsCall, tagParam)
);

// FAILS HERE
var allCall = Expression.Call(
    typeof(Enumerable), "All",
    new[] { typeof(long) },
    searchTagsConstant,
    anyCall
);

No generic method 'All' on type 'System.Linq.Enumerable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.

人们认为它会起作用，因为 Enumerable.All<TSource, Func<TSource, bool>> 应该由 searchTagsConstant 和 anyCall 满足？

Answer 1

t was thought it would work as the Enumerable.All<TSource, Func<TSource, bool>> should be satisfied by the searchTagsConstant and anyCall

没有。 anyCall 不是 lambda 表达式 (Func<TSource, bool>)，只是这种表达式的潜在 body。

让我们从您的目标开始：

IEnumerable<long> searchTags = new List<long>() { 1, 2, 3 };

Expression<Func<Taggable, bool>> lambda = 
    taggable => searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag));

学习如何构建表达式树的最简单方法是在编译时创建示例表达式，然后通过一些反编译器检查生成的代码，或者在运行时通过调试器检查表达式树。

无论如何，请注意上面的表达式有 3 个 lambda 参数，而在你的尝试中你只有 2 个。而且没有 Contains 调用，不知道你为什么放在那里。

构建上面的表达式可以这样：

var taggable = Expression.Parameter(typeof(Taggable), "taggable");
var tag = Expression.Parameter(typeof(Tag), "tag");
var searchTag = Expression.Parameter(typeof(long), "searchTag");
// tag.TagId == searchTag
var anyCondition = Expression.Equal(
    Expression.Property(tag, "TagId"),
    searchTag);
// taggable.Tags.Any(tag => tag.TagId == searchTag)
var anyCall = Expression.Call(
    typeof(Enumerable), nameof(Enumerable.Any), new[] { typeof(Tag) },
    Expression.Property(taggable, "Tags"), Expression.Lambda(anyCondition, tag));
// searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag))
var allCall = Expression.Call(
    typeof(Enumerable), nameof(Enumerable.All), new[] { typeof(long) },
    Expression.Constant(searchTags), Expression.Lambda(anyCall, searchTag));
// taggable => searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag))
var lambda = Expression.Lambda(allCall, taggable);

如何用表达式树表达 All have Any

How to express All have Any with Expression Trees

c#

linq

expression-trees