EF Core 2.1 group by with skip and take

Question

I a currently "paging" through an IQueryable that has many fields { Table1Id, Table1Label, IsActive, ...} and there can be mulitple records in IQueryable result for a PdcId, like the following:

var result = from a in _entities.table1
             join b in _entities.table2 on new { a.Table1Id, a.Table1LevelId } equals new { Table1Id = b.Table2Id, Table1LevelId = b.Table2LevelId }                
             join c in _entities.Table3 on a.Table1Id equals c.Table1Id into cc from ccc in cc.DefaultIfEmpty()            
             where a.Valide == true 
             select new MeteringPointDetailModel
             {
                Table1Id = a.Table1Id,
                Table1Label = a.Label,
                IsActive = a.IsActive,                                     
                Table3Label = ccc.Label,                 
             };

I tried this code but when i see the result generating in sql using sql profiler, the query is running without stop !! (generate multiple sql query ).

var data = await result.Where(i => result.GroupBy(p => p.Table1Id)
                       .Select(t => t.Key)
                       .Skip(query.Page).Take(query.PageSize)
                       .Contains(i.Table1Id)).ToListAsync();

How would I do this if I wanted to first group by Table1Id and then skip and take on the distinct Table1Id.

for example: if I have a result that has two records, one ends up being # 50 and the other 51, if I page by 50, I won't get record 51, and I want it.

Answer 1

That's what i did and worked for me :

Solution 1

var dataTable1 = (from a in _entities.table1 
                  where a.Valide == true 
                  select new {...}).Skip(query.Page).Take(query.PageSize);

var result = from a in dataTable1
         join b in _entities.table2 on new { a.Table1Id, a.Table1LevelId } equals new { Table1Id = b.Table2Id, Table1LevelId = b.Table2LevelId }                
         join c in _entities.Table3 on a.Table1Id equals c.Table1Id into cc from ccc in cc.DefaultIfEmpty()                         
         select new MeteringPointDetailModel
         {
            Table1Id = a.Table1Id,
            Table1Label = a.Label,
            IsActive = a.IsActive,                                     
            Table3Label = ccc.Label,                 
         };

var data = await result.ToListAsync();

Solution 2

var result = from a in _entities.table1
         join b in _entities.table2 on new { a.Table1Id, a.Table1LevelId } equals new { Table1Id = b.Table2Id, Table1LevelId = b.Table2LevelId }                
         join c in _entities.Table3 on a.Table1Id equals c.Table1Id into cc from ccc in cc.DefaultIfEmpty()            
         where a.Valide == true 
         select new MeteringPointDetailModel
         {
            Table1Id = a.Table1Id,
            Table1Label = a.Label,
            IsActive = a.IsActive,                                     
            Table3Label = ccc.Label,                 
         };

result = !string.IsNullOrWhiteSpace(query.Table3Label) ? result.Where(c => c.Table3Label.ToLower().Contains(query.Table3Label.ToLower())) : result;

var table1Ids = await result.OrderBy(p => p.Table1Id)
                            .Select(p => p.Table1Id).Distinct()
                            .Skip(query.Page).Take(query.PageSize)
                            .ToListAsync();

var data = await result.Where(p => table1Ids.Contains(p.Table1Id)).ToListAsync();

Solution 2 is more useful if there are clause condition (search criteria) in join tables as specified in the example.

Hope it will help someone.