将两个LINQ表达式合并为一个

Question

I have created two LINQ queries to extract same type of value, but basing on different references in database.

var productGroupIdList = (from organizationalUnit 
                          in user.OrganizationalUnit
                          from productGroup 
                          in organizationalUnit.ProductGroup
                          select productGroup.ProductGroupId).ToList();
productGroupIdList.AddRange(from subOrganizationalUnit 
                            in user.SubOrganizationalUnit
                            from productGroup 
                            in subOrganizationalUnit.ProductGroup
                            select productGroup.ProductGroupId);

Is there any way to connect them into one LINQ query?

Answer 1

As long as they have the exact same structure, you should be able to use Concat() , which translates to a UNION ALL in SQL.

var productGroupIdList = (from organizationalUnit 
                      in user.OrganizationalUnit
                      from productGroup 
                      in organizationalUnit.ProductGroup
                      select productGroup.ProductGroupId)
                   .Concat(
                        from subOrganizationalUnit 
                        in user.SubOrganizationalUnit
                        from productGroup 
                        in subOrganizationalUnit.ProductGroup
                        select productGroup.ProductGroupId)
                   .ToList();

Answer 2

how about you Concat only a part of both queries: the first part, since the 2nd parts are identical?

var productGroupIdList = from productGroup in 
            (from organizationalUnit in user.OrganizationalUnit
            select organizationalUnit.ProductGroup)
            .Concat(
                from subOrganizationalUnit 
                in user.SubOrganizationalUnit
                select subOrganizationalUnit.ProductGroup)
        select productGroup.ProductGroupId;

or see expanded example where combinedProductGroups are a separate variable (that's 1st part of your query combined for both lists)

class Program
{
    static void Main(string[] args)
    {
        var user = new User();

        var combinedProductGroups = (from organizationalUnit
                in user.OrganizationalUnit
                select organizationalUnit.ProductGroup)
            .Concat(from subOrganizationalUnit
                in user.SubOrganizationalUnit
                select subOrganizationalUnit.ProductGroup);

        var productGroupIdList = from productGroup in combinedProductGroups
                select productGroup.ProductGroupId;

    }
}

public class User
{
    public List<OrgUnit> OrganizationalUnit;
    public List<SubOrgUnit> SubOrganizationalUnit;
}

public class OrgUnit
{
    public ProdGroup ProductGroup;
}

public class SubOrgUnit
{
    public ProdGroup ProductGroup;
}

public class ProdGroup
{
    public string ProductGroupId;
}

Answer 3

If the tables have the same structure, I am guessing you might be able to

var result = user.OrganizationalUnit.SelectMany(x => x.ProductGroup.ProductGroupId)
  .Concat(user.SubOrganizationalUnit.SelectMany(x => x.ProductGroup.ProductGroupId)).ToList();

Answer 4

Based on all of your answers I made this

var productGroupIdList = (from organizationalUnit 
                          in user.OrganizationalUnit
                          from subOrganizationalUnit
                          in user.SubOrganizationalUnit
                          from productGroup 
                          in organizationalUnit.ProductGroup.Concat(subOrganizationalUnit.ProductGroup)
                          select productGroup.ProductGroupId).Distinct().ToList();

I have also created this using Lambda

user.OrganizationalUnit.SelectMany(x => x.ProductGroup)
    .Concat(user.SubOrganizationalUnit.SelectMany(x => x.ProductGroup))
    .Select(x => x.ProductGroupId)
    .Distinct()
    .ToList()