Sql.Row doesn't work with server-side functions

Sorry to bother, but this is not supported yet:

await Events.Where(x => x.Id == key)
            .Set(d => Sql.Row(d.Title, d.SearchVector),
                t => (from x in Events
                    where t.Id == x.Id
                    select Sql.Row(t.Title, EF
                        .Functions
                        .ToTsVector("test")
                    )).Single())
            .UpdateAsync();

model:

public class Event
{
    [LinqToDB.Mapping.PrimaryKey] public Guid Id { get; set; }
    public string Title { get; set; } = "";
    public NpgsqlTsVector? SearchVector { get; set; } = null;
}

System.InvalidOperationException: The 'ToTsVector' method is not supported because the query has switched to client-evaluation. This usually happens when the arguments to the method cannot be translated to server. Rewrite the query to avoid client evaluation of arguments so that method can be translated to server.
         at Microsoft.EntityFrameworkCore.NpgsqlFullTextSearchDbFunctionsExtensions.ToTsVector(DbFunctions _, String document)
         at lambda_method215(Closure , Expression , IDataContext , Object[] )
         at LinqToDB.Linq.QueryRunner.SetParameters(Query query, Expression expression, IDataContext parametersContext, Object[] parameters, Int32 queryNumber, SqlParameterValues parameterValues)
         at LinqToDB.Linq.QueryRunnerBase.SetCommand(Boolean forGetSqlText)
         at LinqToDB.Data.DataConnection.QueryRunner.ExecuteNonQueryAsync(CancellationToken cancellationToken)
         at LinqToDB.Linq.QueryRunner.NonQueryQueryAsync(Query query, IDataContext dataContext, Expression expression, Object[] ps, Object[] preambles, CancellationToken cancellationToken)
         at LinqToDB.Linq.QueryRunner.NonQueryQueryAsync(Query query, IDataContext dataContext, Expression expression, Object[] ps, Object[] preambles, CancellationToken cancellationToken)
         at LinqToDB.Linq.ExpressionQuery`1.LinqToDB.Async.IQueryProviderAsync.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
         at LinqToDB.LinqExtensions.UpdateAsync[T](IUpdatable`1 source, CancellationToken token)

_Originally posted by @sep2 in https://github.com/linq2db/linq2db/issues/3321#issuecomment-1092875003_

[jods4]

Just to spell it out clearly in case anyone else has similar issues:

Simple expressions can be evaluated anywhere, but some expressions can only be evaluated server-side (i.e. SQL) and some can only be evaluated client-side (i.e. .NET).

Sql.Row is an example of a server-side feature that linq2db can only translate to SQL and never evaluates in C#, esp. in the UPDATE case here.

When linq2db doesn’t know how to translate a complex function to SQL, such as ToTsVector here, it just evaluates it in .NET.

But obviously you can’t mix-and-match both worlds. Putting .net code inside SQL is not possible, so nesting ToTsVector inside Row can’t be executed by linq2db. As @MaceWindu pointed out the solution is to teach linq2db how to translate the client-side code into SQL, e.g. with a custom [Expression] function.

Happy to see people other than me having uses for Sql.Row just one day after release 😃

[MaceWindu]

Simplest one is to use Sql.Expression:

[Sql.Expression("{0} || {1}", ServerSideOnly=true)]
public static NpgsqlTsVector TsVectorConcat(NpgsqlTsVector left, NpgsqlTsVector right) => throw new InvalidOperationException();