ExpressionQueryImpl<TElement>.ToString() doesn't update SQL text when parameter's values changes

Hello, when we build queries with linq2db we get an ExpressionQueryImpl<TElement> object that implements IQueryable<T> interface. For example:

...
DataConnection.DefaultSettings = new MySettings();
Configuration.Sql.GenerateFinalAliases = true;

using var db = new WipDB("Wip");
var wipCte = new WipCte(db);

var ncCodeBo = "NCCodeBO:8110,SETUP_OSCILLOSCO";

var result = from item in wipCte.AllowedNcCode() where item.NcCodeBo == ncCodeBo select item;
var sql = result.ToString();
Console.WriteLine(sql);
..

Output:

-- Wip Oracle.Managed Oracle
DECLARE @ncCodeBo_1 Varchar2(30) -- String
SET     @ncCodeBo_1 = 'NCCodeBO:8110,SETUP_OSCILLOSCO'

WITH AllowedNcCode (Handle, NcCodeColumn, Description)
AS
(
        SELECT DISTINCT
                ncCode.HANDLE as NcCodeBo,
                ncCode.NC_CODE as NcCode,
                ncCode.DESCRIPTION as NcCodeDescription
        FROM
                WIPUSER.NC_CODE ncCode
                        INNER JOIN WIPUSER.NC_GROUP_MEMBER ncGroupMember ON ncCode.HANDLE = ncGroupMember.NC_CODE_OR_GROUP_GBO
        WHERE
                ((ncGroupMember.NC_GROUP_BO IS NOT NULL AND ncGroupMember.NC_GROUP_BO = 'NCGroupBO:' || ncCode.SITE || ',CATAN_AUTO' OR ncGroupMember.NC_GROUP_BO IS NOT NULL AND ncGroupMember.NC_GROUP_BO = 'NCGroupBO:' || ncCode.SITE || ',CATAN_MAN') OR ncGroupMember.NC_GROUP_BO IS NOT NULL AND ncGroupMember.NC_GROUP_BO = 'NCGroupBO:' || ncCode.SITE || ',CATAN_ALL')
)
SELECT
        item.Handle,
        item.NcCodeColumn,
        item.Description
FROM
        AllowedNcCode item
WHERE
        item.Handle = :ncCodeBo_1

If I change ncCodeBo and I print the SQL, I get the previous one because the SQL query is built when I assign the query to the variable result:

ncCodeBo = "NCCodeBO:8110,SETUP_OSCILLOSCO2";
sql = result.ToString();
Console.WriteLine(sql);

-- Wip Oracle.Managed Oracle
DECLARE @ncCodeBo_1 Varchar2(30) -- String
SET     @ncCodeBo_1 = 'NCCodeBO:8110,SETUP_OSCILLOSCO' -- It should change to "NCCodeBO:8110,SETUP_OSCILLOSCO2"

WITH AllowedNcCode (Handle, NcCodeColumn, Description)
AS
...

My question is: is there a way to get an ExpressionQueryImpl<TElement> with a method to call to set only the changing part of the query? For example the parameter ncCodeBo?

If the query is really huge, rebuilding the query only to change few parameters is time consuming.

Thank you!

[sdanyliv]

It is a bug in ToString(), we have to repopulate parameters for this call. Will fix that. First query is slow because we parse Expression Tree and provide optimizations. Second query just reuse parsed AST and generated SQL.

[filippobottega]

Hello @sdanyliv , Sorry, I don’t really need to log “all queries”, and sometime I need the SQL query without running the query. I have created this workaround that works very well:

DataConnection.DefaultSettings = new MySettings();
Configuration.Sql.GenerateFinalAliases = true;

using var db = new WipDB("Wip");
var wipCte = new WipCte(db);

var ncCodeBo = "NCCodeBO:8110,SETUP_OSCILLOSCO";

var queryBuilder = (Func<IQueryable<AllowedNcCodeOutput>>) (() =>  from item in wipCte.AllowedNcCode() where item.NcCodeBo == ncCodeBo select item);
var result = queryBuilder.Invoke();
var sql = result.ToString(); // Very slow...
Console.WriteLine(sql);

ncCodeBo = "NCCodeBO:8110,SETUP_OSCILLOSCO2";
result = queryBuilder.Invoke();
sql = result.ToString(); // Very fast!
Console.WriteLine(sql);

I have discovered that only the first call to result.ToString() is slow but the second call is fast and gives me the right result. You should probably update the documentation to explain the ToString() behavior and to show how to update the ToString() result if parameters change.