Re: How to create an expression?
Re: How to create an expression?
- Subject: Re: How to create an expression?
- From: Dave DeLong <email@hidden>
- Date: Mon, 26 Sep 2011 10:45:00 -0700
I don't think it's possible without a format string.
"$x.firstName" gets turned into an expression of type NSFunctionExpression. The operator is a variable expression, and the first argument is an expression with a private type (10). gdb shows that the class of that argument is "NSKeyPathSpecifierExpression", but there doesn't appear to be a way to create one programmatically without a format string.
Similarly, the SUBQUERY(...).@count gets turned into a FUNCTION() expression. The operand is the subquery expression, and the first argument is another expression of type 10.
I think you're out of luck and will have to build a format string and pass that to predicateWithFormat:. I'd probably file a bug requesting more API if I were you.
HTH,
Dave
On Sep 26, 2011, at 7:05 AM, Willeke wrote:
> hi,
>
> How do I programmatically create the $x.firstname and .@count parts of this expression?
> SUBQUERY(residents, $x, $x.firstname == "Jane" && $x.lastname == "Doe").@count
>
> When I create a subquery predicate with predicateWithFormat:, the class of the $x.firstname and .@count expressions is NSKeyPathExpression and the type is NSFunctionExpressionType. The operand is an expression of type NSVariableExpressionType or NSSubqueryExpressionType. The function is valueForKeyPath:.
>
> When I create an expression with expressionForKeyPath:, the operand is SELF instead of the variable or the subquery. When I create an expression with expressionForFunction:selectorName:arguments:, the class is NSFunctionExpression. When the argument is a keypath expression, instead of $x.firstname the expression tries to evaluate $x.Jane and that doesn't work. executeFetchRequest throws an exception: -constantValue only defined for abstract class. Define -[NSKeyPathExpression constantValue]!
> If the argument is a constant value expression, executeFetchRequest throws an exception: -keyPath only defined for abstract class. Define -[NSConstantValueExpression keyPath]!.
>
> The predicate will be edited in a rule editor so I have to convert it to criteria and back.
> The predicate will be used as filter predicate of an array controller in entity mode and/or in a fetch request with Core Data (SQLite).
>
> Thanks,
> Willeke
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