EF6 with ODP 12cR3 : ORA-12704 (VARCHAR2 not supported?)

Question

         Hi!
          We cannot port our working code from EF5 to EF 6.1.2, because the generated SQL output unicode query which is not compatible with VARCHAR2 column.
          How can we fix this issue ?
            Our Setup
             Oracle 11.2.0.3.0
             NLS_CHARACTERSET               WE8MSWIN1252                            
             NLS_NCHAR_CHARACTERSET         AL16UTF16
                -- TEST
                  CREATE TABLE "TEST"
                   ( "ID" NUMBER(*,0) NOT NULL ENABLE,
                 "NAME" VARCHAR2(20),
                 "VALUE" VARCHAR2(20)
                   ) PCTFREE 10 INITRANS 1 NOCOMPRESS LOGGING
                  STORAGE( INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
                -- ID
                ALTER TABLE "TEST" ADD CONSTRAINT "ID" PRIMARY KEY ("ID") ENABLE;
             Objective : Trying to port working code from EF5 to EF6.1.2
             Problem : Generated SQL contains unicode query when using VARCHAR2 column type.
            using (var ctx = new Entities())
                var queryable = ctx.TESTs.Where(x => x.NAME.Contains("test")).Select(
                    t => new
                        TestVarcharVsUnicode = t.VALUE + "AnotherStringLiteralWillGenerateNvarcharSQL"
                /* Generated SQL
                queryable =
                    SELECT
                    1 AS "C1",
                    ((CASE WHEN ("Extent1"."VALUE" IS NULL) THEN N'' ELSE "Extent1"."VALUE" END)||('AnotherStringLiteralWillGenerateNvarcharSQL')) AS "C2"
                    FROM "TES_RA"."TEST" "Extent1"
                    WHERE ("Extent1"."NAME" LIKE '%test%')
                var result = queryable.ToList();   // ORA-12704: character set mismatch here because VALUE column type is VARCHAR2 not NVARCHAR2
UPDATE: By using an IDbCommandInterceptor class we can replace those Unicode string before execution.  But it's only a workaround until we found the correct way to fix it.
Thank you in advance,
Jean Francoeur

Answer 1

Hi Verolamaz,
No update on our side.
We've also tried modelBuilder.Properties<string>().Configure(c => c.HasColumnType("varchar2"));
But the generated SQL stay the same...
Jean