Question

We have a form which allows users to specify criteria to query a database.

Our form builds “criterion” objects which are then used to build the nHibernate criteria.

Our current code to do this is:

public virtual ICriteria BuildCriteria(ICriteria criteria)
{
    foreach (SheCriterion criterion in this.SheCriterions)
    {
        if (criterion.OperatorKey == "OR")
        {
            //// code required here to process ORs
        }
        criteria.Add(criterion.BuildCriterion());
    }
    return criteria;
}

Unfortunately, this is where I’m stuck – if we AND each criterion there is no problem but I’m having difficulties in working out how to add ORs – by the time we know that an OR is involved, the previous criterion has already been processed.

Can anyone help?

Answer 1

or is not that easy. Consider a and b or c there are 2 different possibilities (a and b) or c and a and (b or c) so if a = false you’ll get two different answers. You’ll have to build a tree of criterias and in

public virtual ICriteria BuildCriteria(ICriteria criteria)
{
    foreach (SheCriterion criterion in this.SheCriterions)
    {
        criteria.Add(criterion.BuildCriterion());
    }

    return criteria;
}

public virtual ICriterion BuildCriterion()
{
    if (OperatorKey == "OR")
    {
        return new Disjunction()
            .Add(Left.BuildCriterion())
            .Add(right.BuildCriterion());
    }
    else
    {
        return new Conjunction()
            .Add(Left.BuildCriterion())
            .Add(right.BuildCriterion());
    }
}

Update: you’ll need a tree otherwise

Man { Name = "Bill", Eyecolor = "blue", Height = 175, IsRich = true };

// will show Bill
SELECT * FROM Men WHERE height > 180 AND eyecolor = blue OR IsRich = 1
SELECT * FROM Men WHERE (height > 180 AND eyecolor = blue) OR IsRich = 1

// will not show Bill
SELECT * FROM Men WHERE height > 180 AND (eyecolor = blue OR IsRich = 1)