Hi,
I am trying to create a custom Hql Generator for Collection Contains which
would allow generating Hql from Linq's Contains overload with
IEqualityComparer. It should behave same as CollectionContains on SQL
server, but when expression tree is compiled and executed in memory, I
would like to be able to compare stings
with StringComparer.OrdinalIgnoreCase.
Essentially I have a working statement
a => operatorIds.Contains(a.OperatorId);
which I want to turn into
a => operatorIds.Contains(a.OperatorId, StringComparer.OrdinalIgnoreCase);
I found source code for Collection Contains and modified it like this:
public class CollectionContainsWithComparerGenerator :
BaseHqlGeneratorForMethod
{
public CollectionContainsWithComparerGenerator()
{
SupportedMethods = new[]
{
ReflectionHelper.GetMethodDefinition(() =>
Enumerable.Contains<object>(null, null, null)),
};
}
public override HqlTreeNode BuildHql(MethodInfo method, Expression
targetObject, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder
treeBuilder, IHqlExpressionVisitor visitor)
{
// TODO - alias generator
HqlAlias alias = treeBuilder.Alias("x");
ParameterExpression param = Expression.Parameter(targetObject.Type, "x");
HqlWhere where = treeBuilder.Where(visitor.Visit(Expression.Lambda(
Expression.Equal(param, arguments[0]), param))
.AsExpression());
return treeBuilder.Exists(
treeBuilder.Query(
treeBuilder.SelectFrom(
treeBuilder.From(
treeBuilder.Range(
visitor.Visit(targetObject),
alias)
)
),
where));
}
}
Basically, I kept the *BuildHql() *method AS-IS and only modified signature
for *SupportedMethod*. However, this generator throws null reference
exception because *targetObject* is null.
I noticed that some generators use *targetObject *while others only use
*arguments
*but I still can't figure out why my generator won't work although it's
identical to CollectionContainsGenerator and how to modify it to fix.
Any suggestions will help. I couldn't find any documentation on how to
build custom Hql generators.
Thanks
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