Ef core could not translate my custom sql server STRING_AGG function - sql-server

Question

String.Join in efcore not support and I want to get list of string with separator like sql function String_Agg
I tried to create custom sql server function but i get this error:
The parameter 'columnPartArg' for the DbFunction 'QueryHelper.StringAgg(System.Collections.Generic.IEnumerable`1[[System.String, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=]],System.String)' has an invalid type 'IEnumerable'. Ensure the parameter type can be mapped by the current provider.
This is my function and OnModelCreatingAddStringAgg for register it in my dbcontext
public static string StringAgg(IEnumerable<string> columnPartArg, [NotParameterized] string separator)
{
throw new NotSupportedException();
}
public static void OnModelCreatingAddStringAgg(ModelBuilder modelBuilder)
{
var StringAggFuction = typeof(QueryHelper).GetRuntimeMethod(nameof(QueryHelper.StringAgg), new[] { typeof(IEnumerable<string>), typeof(string) });
var stringTypeMapping = new StringTypeMapping("NVARCHAR(MAX)");
modelBuilder
.HasDbFunction(StringAggFuction)
.HasTranslation(args => new SqlFunctionExpression("STRING_AGG",
new[]
{
new SqlFragmentExpression((args.ToArray()[0] as SqlConstantExpression).Value.ToString()),
args.ToArray()[1]
}
, nullable: true, argumentsPropagateNullability: new[] { false, false }, StringAggFuction.ReturnType, stringTypeMapping));
}
and this code run above function
_context.PersonnelProjectTimeSheets.GroupBy(c => new { c.Date.Date, c.PersonnelId, c.Personnel.PersonnelCode, c.Personnel.FirstName, c.Personnel.LastName})
.Select(c => new PersonnelProjectTimeOutputViewModel
{
IsConfirmed = c.Min(c => (int)(object)(c.IsConfirmed ?? false)) == 1,
PersonnelDisplay = c.Key.PersonnelCode + " - " + c.Key.FirstName + " " + c.Key.LastName,
PersonnelId = c.Key.PersonnelId,
Date = c.Key.Date,
ProjectName = QueryHelper.StringAgg(c.Select(x=>x.Project.Name), ", "),
TotalWorkTime = 0,
WorkTimeInMinutes = c.Sum(c => c.WorkTimeInMinutes),
});
And also i change my StringAgg method input to
string columnPartArg
and change SqlFunctionExpression of OnModelCreatingAddStringAgg to
new[]
{
new SqlFragmentExpression((args.ToArray()[0] as
SqlConstantExpression).Value.ToString()),
args.ToArray()[1]
}
and change my query code to
ProjectName = QueryHelper.StringAgg("Project.Name", ", ")
now when run my query, sql server could not recognize the Project

Answer 1

i guess the parameter 'columnPartArg' of dbfunction 'STRING_AGG' is varchar or nvarchar. right?
most database function or procedure has not table value as parameter.
in this case,use EFCore's 'client evaluation' is good sulution. linq like below：
_context.PersonnelProjectTimeSheets.GroupBy(c => new { c.Date.Date, c.PersonnelId, c.Personnel.PersonnelCode, c.Personnel.FirstName, c.Personnel.LastName})
.Select(c => new PersonnelProjectTimeOutputViewModel
{
IsConfirmed = c.Min(c => (int)(object)(c.IsConfirmed ?? false)) == 1,
PersonnelDisplay = c.Key.PersonnelCode + " - " + c.Key.FirstName + " " + c.Key.LastName,
PersonnelId = c.Key.PersonnelId,
Date = c.Key.Date,
ProjectName = string.Join(", ",c.Select(x=>x.Project.Name)),//Client evaluation
TotalWorkTime = 0,
WorkTimeInMinutes = c.Sum(c => c.WorkTimeInMinutes),
});