How do I concatenate the items from the list into a comma delimited string in LINQ

Question

I have this subquery which is part of a larger query. I want the column called ErrorType in the left hand side to be populated by comma delimited set of values returned by the List on the right hand side. How can i do it ? ErrorTypes is a master whose Key is ErrorTypeID and Value is ErrorTypeName. ProductionErrors is the transaction table whose key is Production ID (supplied by outer query), and whose matching key is ErrorType.

ErrorType =  (from errorType in db.ErrorTypes 
              join prdErrType in db.ProductionErrors 
              on errorType.ErrorTypeID equals prdErrType.ErrorTypeID
              where prdErrType.ProductionID==prd.ProductionID
              select errorType.ErrorTypeName).ToList();

Answer 1

在这种情况下，最好使用string.Join ：

ErrorType = string.Join(",", (from...)); // you can omit .ToList() perhaps

Answer 2

you should query something like::

ErrorType =  (from errorType in db.ErrorTypes join prdErrType in db.ProductionErrors on errorType.ErrorTypeID equals prdErrType.ErrorTypeID
                                              where prdErrType.ProductionID==prd.ProductionID
                                              select new 
                                              {
                                               ErrorType=errorType.ErrorTypeName.tostring()+','
                                               }).ToList()

This is because sometimes LINQ to SQL doesn't support string functions.

Answer 3

string.Join is the way I would do this, as in the answers that have already been given. But as with most things, there are multiple ways to do it. Another way is using the IEnumerable<T>.Aggregate method:

var query = (from errorType in db.ErrorTypes 
             join prdErrType in db.ProductionErrors 
             on errorType.ErrorTypeID equals prdErrType.ErrorTypeID
             where prdErrType.ProductionID==prd.ProductionID
             select errorType.ErrorTypeName);

string errorType = query.Aggregate((result,next) => result + "," + next);