当两个列表的类型不同时，如何将每个循环的嵌套转换为Linq

Question

I want to convert a nested foreach loop in C# to Linq. I know how to do it if the two lists are of same type. But in my case, they are of different type, except that they both have two common properties, DocumentId and IsValid. I have to loop through the outer list and the inner list and whenever the DocumentId of both are the same, then assign the IsValid value from the outer loop object to the inner loop object. I have the following foreach loop is working fine.

foreach (var docs in outerDocuments)
{
     foreach (var presentedDocuments in innerdocuments)
     {
           if (docs.DocumentId.Equals(presentedDocuments.DocumentId))
           {
                 presentedDocuments.IsValid = docs.IsValid;
           }
     }
}

I need to convert it to Linq. Usually ReSharper does a good job of refactoring such code. But in this case it converted only the nested foreach to Linq, and even then it threw a warning , "Access to foreach variable in closure".

Thanks

Answer 1

You can try using Enumerable.Join :

foreach (var item in outerDocuments.Join(innerdocuments,
                                         outer => outer.DocumentId,
                                         inner => inner.DocumentId,
                                         (outer, inner) => new { OuterDoc = outer, InnerDoc = inner }))
{
    item.InnerDoc.IsValid = item.OuterDoc.IsValid;
}

Answer 2

Try this:

foreach (var presentedDocuments in innerdocuments)
{
    var doc = outerDocuments.FirstOrDefault(a => a.DocumentId.Equals(presentedDocuments.DocumentId));
    if (doc != null)
    {
        presentedDocuments.IsValid = doc.IsValid;
    }
}

Answer 3

You can use .Join() extension method and do it in one line like this:

outerDocuments.Join(innerDocuments, o => o.DocumentId, i => i.DocumentId, (o, i) =>  i.IsValid = o.IsValid).ToList();

As noted by @sstan .ToList() call is required to force enumeration.