EF Core 2.1 group by with skip and take

Question

我目前 "paging" 通过具有许多字段 {Table1Id、Table1Label、IsActive、...} 的 IQueryable，并且在 PdcId 的 IQueryable 结果中可以有多个记录，如下所示：

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,                 
             };

我尝试了这段代码，但是当我看到使用 sql 探查器在 sql 中生成的结果时，查询是运行不停！！（生成多个 sql 查询）。

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();

如果我想先按 Table1Id 分组，然后跳过并采用不同的 Table1Id，我该怎么做。

例如：如果我的结果有两条记录，一条最终是 #50，另一条是 51，如果我按 50 分页，我不会得到记录 51，我想要它。

Answer 1

这就是我所做的和为我工作的:

解决方案 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();

解决方案 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();

如果示例中指定的连接表中存在子句条件（搜索条件），则方案2更有用。

希望对大家有所帮助。

EF Core 2.1 group by with skip and take

EF Core 2.1 group by with skip and take

c#

linq

c#-6.0

ef-core-2.1