Hello I'm trying to create my own expression type to allow the use of Daypart MSSQL function. I've taken example on the source code (Expression class) but I still have a (big?) problem.

Ok so here is my source code :

constructor :

public DatePartExpression(DatePartType type, ExOp operatorToUse, IEntityField2 rightOperand)
{
    InitClass();
    _rightOperand   = new ExpressionFieldElement(ExpressionElementType.Field, rightOperand, null);
    _operator       = operatorToUse;
    _type       = type;
}

public virtual string ToQueryText(ref int uniqueMarker, bool inHavingClause)
        {
            if(_creator==null)
            {
                throw new System.ApplicationException("DatabaseSpecificCreator object not set. Cannot create query part.");
            }

            StringBuilder queryText = new StringBuilder(128);
            _parameters.Clear();


            if (this.RightOperand != null) 
            {
                string leftOp   = this.ToDatePartText(this._type);
                [b]string rightOp   = this.OperandToText(ref queryText, this._rightOperand, ref uniqueMarker, false, inHavingClause);[/b]               
                queryText.AppendFormat(null, "DATEPART({0}, {1})", leftOp, rightOp);
            }

            return queryText.ToString();
        }

The original method a bit modified to return the text instead of append to the queryBuildler :

private string OperandToText(ref StringBuilder queryText, IExpressionElement operand, ref int uniqueMarker, bool isLeftOperand, bool inHavingClause)
        {
            IExpressionFieldElement fieldElement = null;

            switch(operand.Type)
            {
                case ExpressionElementType.Value:
                    IDataParameter parameter = _creator.CreateParameter("LO" + operand.GetHashCode().ToString(), ParameterDirection.Input, operand.Contents);
                    _parameters.Add(parameter);
                    uniqueMarker++;
                    parameter.Value = operand.Contents;
                    parameter.ParameterName += uniqueMarker.ToString();
                    return parameter.ParameterName;
                case ExpressionElementType.Field:
                    fieldElement = (ExpressionFieldElement)operand;
                    IEntityFieldCore fieldCore = (IEntityFieldCore)fieldElement.Contents;
                    if(fieldCore.ExpressionToApply!=null)
                    {
                        // add parameters to this expression's collection.
                        _parameters.AddRange(fieldCore.ExpressionToApply.Parameters);
                    }
                    [b][colorvalue="FF0000"]return string.Format("{0}", _creator.CreateFieldName(fieldCore, fieldElement.PersistenceInfo, fieldCore.Name, fieldCore.ObjectAlias, ref uniqueMarker, inHavingClause));[/color][/b]                case ExpressionElementType.Expression:
                    IExpression expressionToConvert = (IExpression)operand.Contents;
                    // pass on the name creator object
                    expressionToConvert.DatabaseSpecificCreator = _creator;
                    _parameters.AddRange(expressionToConvert.Parameters);
                    return string.Format("({0})", expressionToConvert.ToQueryText(ref uniqueMarker, inHavingClause));
            }
            throw new ArgumentException("Invalid ExpressionElementType:" + operand.Type.ToString());
        }

Ok now the problem is :

TestCase 'M:HRAccent.HRATestCenter.HRABusinessLayer.llblgen.DatePartExpressionTest.TestDatePart' failed: Object reference not set to an instance of an object. System.NullReferenceException: Object reference not set to an instance of an object. at SD.LLBLGen.Pro.DQE.SqlServer.SqlServerSpecificCreator.CreateFieldName(IFieldPersistenceInfo persistenceInfo, String fieldName, String objectAlias, Boolean appendAlias) at SD.LLBLGen.Pro.DQE.SqlServer.SqlServerSpecificCreator.CreateFieldName(IEntityFieldCore fieldCore, IFieldPersistenceInfo persistenceInfo, String fieldName, String objectAlias, Int32& uniqueMarker, Boolean applyAggregateFunction) p:\hraccentsolution\hraccentserver\hrabusinesslayer\llblgen\datepartexpression.cs(225,0): at HRAccent.BusinessLayer.Llblgen.DatePartExpression.OperandToText(StringBuilder& queryText, IExpressionElement operand, Int32& uniqueMarker, Boolean isLeftOperand, Boolean inHavingClause)

It crash when executing this line of code :

return string.Format("{0}", _creator.CreateFieldName(fieldCore, fieldElement.PersistenceInfo, fieldCore.Name, fieldCore.ObjectAlias, ref uniqueMarker, inHavingClause));

In debug mode, I see fieldElement.PersistenceInfo is null but : - I don't know why - I don't know how to fill it ?

The unit test using the expression :

public void TestDatePart() 
        {
            IExpression             expDatePart = new DatePartExpression(DatePartType.month, ExOp.None,  EntityFieldFactory.Create(EventFieldIndex.EvBegindate));
            IEntityField2           field       = EntityFieldFactory.Create(EventFieldIndex.EvBegindate);
            field.ExpressionToApply = expDatePart;
            
            IPredicate              expfilter   = new FieldCompareValuePredicate(field, null, ComparisonOperator.Equal, 10);
            
            RelationPredicateBucket filter      = new RelationPredicateBucket();
            filter.PredicateExpression.Add(expfilter);

            EntityCollection        ec          = new EntityCollection(new EventFactory());
            this.Context.Adapter.FetchEntityCollection(ec, filter);
            HRAccent.BusinessLayer.Process.DumpTools.DumpEventList(ec);
        }

Thanks for any help !

groumf, bold and red in the code tag are not interpreted

If you check out DataAccessAdapter.InsertPersistenceInfoObjects(expression), you'll see that the left operand is always a field or an expression. So the left operand requires persistence info always, the right operand only if it's not a value and if it's specified. I think you return from 'LeftOperand' null, which therefore doesnt make the persistence info for the field be set.

Yes it was because of the null leftoperand Thanks for the tip! Now it seem to work