Get return value from ExecuteSqlRaw in EF Core - entity-framework

Question

I have an extremely large table that I'm trying to get the number of rows for. Using COUNT(*) is too slow, so I want to run this query using EF Core:
int count = _dbContext.Database.ExecuteSqlRaw(
"SELECT Total_Rows = SUM(st.row_count) " +
"FROM sys.dm_db_partition_stats st " +
"WHERE object_name(object_id) = 'MyLargeTable' AND(index_id < 2)");
The only problem is that the return value isn't the result of the query, but the number of records returned, which is just 1
Is there a way to get the correct value here, or will I need to use a different method?

Answer 1

Since you only need a scalar value you can also use an output parameter to retrieve the data, eg
var sql = #"
SELECT #Total_Rows = SUM(st.row_count)
FROM sys.dm_db_partition_stats st
WHERE object_name(object_id) = 'MyLargeTable' AND(index_id < 2)
";
var pTotalRows = new SqlParameter("#Total_Rows", System.Data.SqlDbType.BigInt);
pTotalRows.Direction = System.Data.ParameterDirection.Output;
db.Database.ExecuteSqlRaw(sql, pTotalRows);
var totalRos = (long?)(pTotalRows.Value == DBNull.Value ? null:pTotalRows.Value) ;

Answer 2

If one let's me to recreate a correct answer based on this blog: https://erikej.github.io/efcore/2020/05/26/ef-core-fromsql-scalar.html
We need to create a virtual entity model for our database, that will contain our needed query result, at the same time we need a pseudo DbSet<this virtual model> to use ef core FromSqlRaw method that returns data instead of ExecuteSqlRaw that just returns numbers of rows affected by query.
The example is for returning an integer value, but you can easily adapt it:
Define a return value holding class
public class IntReturn
{
public int Value { get; set; }
}
Fake a virtual DbSet<IntReturn> it will not be really present in db:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
...
modelBuilder.Entity<IntReturn>().HasNoKey();
base.OnModelCreating(modelBuilder);
}
Now we can call FromSqlRaw for this virtual set. In this example the calling method is inside MyContext:DbContext, you'd need to instantiate your own context to use it instead of this):
NOTE the usage of "as Value" - same name as IntReturn.Value property. In some wierd cases you'd have to do the opposite: name your virtual model property after the name of the value thre database funstion is returning.
public int ReserveNextCustomerId()
{
var sql = $"Select nextval(pg_get_serial_sequence('\"Customers\"', 'Id')) as Value;";
var i = this.Set<IntReturn>()
.FromSqlRaw(sql)
.AsEnumerable()
.First().Value;
return i;
}