LINQ联盟在具有相同字段的两个表之间然后在集合中返回

Question

I have given up trying to create a linq query to retrieve a sql server view which is a union between two tables. I will now try to create a linq union.

I have two views, MemberDuesPaid and MemberDuesOwed. They have the same fields in both; (BatchNo, TranDate, DebitAmount, CreditAmount, ReceiptNo, CheckNo, SocSecNo).

I also have a helper class in my application which is called MemberTransaction. It has all the same properties.

How how do i do a union between the two tables where socSecNo = the ssn passed in? I want to union the two tables and return an IEnumerable collection of MemberTransaction. After the two tables are unioned together i want to have the collection that is returned ordered by trandate in descending order.

Answer 1

You can do it in a Linq Union query:

var infoQuery =
    (from paid in db.MemberDuesPaid 
    select new MemberTransaction() {
        BatchNo = paid.BatchNo,
        TranDate = paid.TranDate,
        DebitAmount = paid.DebitAmount,
        CreditAmount = paid.CreditAmount,
        ReceiptNo = paid.ReceiptNo,
        CheckNo = paid.CheckNo,
        SocSecNo = paid.SocSecNo})
    .Union
        (from owed in db.MemberDuesOwed
        select new MemberTransaction() {
        BatchNo = owed.BatchNo,
        TranDate = owed.TranDate,
        DebitAmount = owed.DebitAmount,
        CreditAmount = owed.CreditAmount,
        ReceiptNo = owed.ReceiptNo,
        CheckNo = owed.CheckNo,
        SocSecNo = owed.SocSecNo});

That should return you a set with everything combined into a single list.

[Edit]

If you want distinct values, you can do something like this after the above statement (you can do it inline if you bracket everything, but this is simpler to explain):

infoQuery = infoQuery.Distinct();

The variable infoQuery will by this time be populated entirely with objects of type MemberTransaction rather than the two disparate types in the union statement.

Answer 2

Assuming you've got two collections, one representing each view:

var paid = new List<MemberDuesPaid>();

var owed = new List<MemberDuesOwed>();

Convert both collections above to instances of the third class before performing the union:

var everyone
    = paid.Select(x => new MemberTransaction { BatchNo = x.BatchNo, ... })
          .Union(owed.Select(x => new MemberTransaction { BatchNo = x.BatchNo, ... }))
          .Where(x => x.SocSecNo == ssn)
          .OrderByDescending(x => x.TranDate)
          .ToList();

Now you've got a collection of MemberTransaction , but there's nothing to indicate how one MemberTransaction equals another. So if you just run the above, you'll end up with everything from both collections in the result, instead of a true union.

You have to tell it what makes two instance equal, by implementing IEquatable<T> on the MemberTransaction class.

public class MemberTransaction : IEquatable<MemberTransaction>
{
    public int BatchNo { get; set; }
    public DateTime TranDate { get; set; }
    public decimal DebitAmount { get; set; }
    public decimal CreditAmount { get; set; }
    public int ReceiptNo { get; set; }
    public int CheckNo { get; set; }
    public int SocSecNo { get; set; }

    public bool Equals(MemberTransaction other)
    {
        return BatchNo == other.BatchNo
               && TranDate.Equals(other.TranDate)
               && DebitAmount == other.DebitAmount
               && CreditAmount == other.CreditAmount
               && ReceiptNo == other.ReceiptNo
               && CheckNo == other.CheckNo
               && SocSecNo == other.SocSecNo;
    }
}