In order to perform a simple query with multiple aggregate functions in the select, such as:
select SUM(Value1), SUM(Value2)
from [Table]
I am using "group by (constant value)":
var r = (from x in db.Table
group x by 1 into g
select new
{
Sum1 = g.Sum(x => x.Value1),
Sum2 = g.Sum(x => x.Value2),
}).First();I noted that in EF7 this produces warning CoreEventId.FirstWithoutOrderByAndFilterWarning ("The query uses the 'First'/'FirstOrDefault' operator without 'OrderBy' and filter operators. ...").
Questions
- Is this the correct way to perform such queries in EF7, or is there another way that produces better SQL (see below for a complete example with the SQL generated by EF7)?
- Shouldn't the warning be avoided in these cases (grouping on a constant value), since there will be at most one record in the result?
- Currently, in order to avoid the warning, is there a better way, other than adding "orderby 1" ?
Example console app
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using var db = new TestDb();
var qry = from x in db.Table
group x by 1 into g
select new
{
Sum1 = g.Sum(x => x.Value1),
Sum2 = g.Sum(x => x.Value2),
};
Console.WriteLine(qry.ToQueryString());
var result = await qry.FirstAsync();
Console.WriteLine($"{result.Sum1} {result.Sum2}");
class Table
{
public int Id { get; set; }
public int Value1 { get; set; }
public int Value2 { get; set; }
}
class TestDb : DbContext
{
public DbSet<Table> Table { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer("Server=localhost;Database=Test;Trusted_Connection=True;Encrypt=False");
optionsBuilder.LogTo(Console.WriteLine, LogLevel.Warning);
}
}Output of the example app
SELECT COALESCE(SUM([t0].[Value1]), 0) AS [Sum1], COALESCE(SUM([t0].[Value2]), 0) AS [Sum2]
FROM (
SELECT [t].[Value1], [t].[Value2], 1 AS [Key]
FROM [Table] AS [t]
) AS [t0]
GROUP BY [t0].[Key]
warn: 06/12/2022 09:00:12.252 CoreEventId.FirstWithoutOrderByAndFilterWarning[10103] (Microsoft.EntityFrameworkCore.Query)
The query uses the 'First'/'FirstOrDefault' operator without 'OrderBy' and filter operators. This may lead to unpredictable results.
6 60
Provider and version information
EF Core version: 7.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 7.0
In order to perform a simple query with multiple aggregate functions in the select, such as:
I am using "group by (constant value)":
I noted that in EF7 this produces warning CoreEventId.FirstWithoutOrderByAndFilterWarning ("The query uses the 'First'/'FirstOrDefault' operator without 'OrderBy' and filter operators. ...").
Questions
Example console app
Output of the example app
Provider and version information
EF Core version: 7.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 7.0