ServiceStack.OrmLite：在 SqlExpression 中为匿名类型使用别名

Question

I am posting this question here, as I'm still waiting for approval on the ServiceStack customer forum. It's a rather specific question, so I don't expect many can help... @mythz :)

I'm migrating ServiceStack from v5.4 to v5.7 and there is an issue with aliases in SqlExpression .

I wrote a custom sql concat to get a "kind-of-csv-format" in one column, to merge data into one column, when using unions. From the SQL side, simplified version would be:

SELECT CONCAT(Col1, ',', Col2) as Data FROM Table1
UNION ALL
SELECT CONCAT(Col3, ',', Col4, ',', Col5) as Data FROM Table2

In C#, using OrmLite api, I do:

                var q1 = db.From<Table1>();
                q1.Select(x => new
                {
                    Data = Sql.Custom(q1.ConcatWithSeparator("@delimiter", y => new { y.Col1, y.Col2 }))
                });

ConcatWithSeparator is my custom method, that calls the underlying IOrmLiteDialectProvider.SqlConcat() under the hood, inserting before the @delimiter between the members of anonymous types.

That gave me: SELECT CONCAT("Table1"."Col1", @delimiter, "Table1"."Col2") AS DATA FROM "Table1"

This worked well for the v5.4, but as I noticed, in v5.7, there was a change introduced in method SqlExpression.SetAnonTypePropertyNamesForSelectExpression() ( https://github.com/ServiceStack/ServiceStack.OrmLite/blob/v5.7/src/ServiceStack.OrmLite/Expressions/SqlExpression.cs )

            if (arg is ConditionalExpression ce ||                           // new { Alias = x.Value > 1 ? 1 : x.Value }
                arg is BinaryExpression      be ||                           // new { Alias = x.First + " " + x.Last }
                arg is MemberExpression      me ||                           // new { Alias = DateTime.UtcNow }
                arg is ConstantExpression ct)                                // new { Alias = 1 }
            {
                IOrmLiteConverter converter;
                var strExpr = !(expr is PartialSqlString) && (converter = DialectProvider.GetConverterBestMatch(expr.GetType())) != null
                    ? converter.ToQuotedString(expr.GetType(), expr)
                    : expr.ToString();

                return new PartialSqlString(strExpr + " AS " + member.Name);
            } 

In particular, it's about this check:

            if (
                ...
                arg is MemberExpression      me ||                           // new { Alias = DateTime.UtcNow }
                ...
                ) 

This evaluates to true also for new { x.Col1 } , as it's a short for new { Col1 = x.Col1 } which further makes the sql syntax Col1 as Col1

In my concat, it results in a wrong SQL SELECT CONCAT("Table1"."Col1" AS Col1, @delimiter, "Table1"."Col2" AS Col2) AS DATA FROM "Table1"

So the real question is, shouldn't there be an extra check, that if it's a MemberExpression me , also me.Member.Name.= member.Name ? Or maybe some extra configuration option to bypass the alias generation?

Or... is there any other, easier approach to achieve, what am I trying to do? (I have to support MySQL, MSSQL, Sqlite and PostgreSQL).

Update, regarding @mythz answer below

Unfortunately, it's still not working as expected. But I think, we are getting closer. The converter here:

IOrmLiteConverter converter;
var strExpr = !(expr is PartialSqlString) && (converter = DialectProvider.GetConverterBestMatch(expr.GetType())) != null
    ? converter.ToQuotedString(expr.GetType(), expr)
    : expr.ToString();

return new PartialSqlString(strExpr != member.Name
    ? strExpr + " AS " + member.Name
    : strExpr);

evaluates the expression to quoted string, so in the end there is a check "\"Col1\"" != "Col1" .

Additionally, I also wrote a version of ConcatWithSeparator<Table1, Table2> that can take a lambda as (t1, t2) => new { t1.Col1, t2.Col1 } . In that case, it will evaluate member expression into something like "Table1"."Col1" (depending on DBMS) - I hope, multi-table version is not a hit-in-the-wall and it still can be implemented without raw sql...

Answer 1

I've changed it to not use the alias when the alias is the same name in this commit .

This change is available from the latest v5.7.1 that's now available on MyGet .