What is the best way to build a complex NSCompoundPredicate?

Question

I need to build an NSPredicate with many pieces of data. For example in SQL I would do something like the following:

SELECT * 
  FROM TRANSACTIONS
         


        

Answer 1

What you need to do is to create a Predicate for each one of your clauses. For example let's break down your query:

1. SELECT * FROM TRANSACTIONS
2. WHERE CATEGORY IN (categoryList)
3. AND LOCATION IN (locationList)
4. AND TYPE IN (typeList)
5. AND NOTE contains[cd] "some text"
6. AND DATE >= fromDate AND DATE <+ toDate

Based on this, you have 5 predicates (2-6). So let's work on them one by one.

 NSPredicate *inCategoryPredicate = [NSPredicate predicateWithFormat:@"Category IN %@", categoryList];

 NSPredicate *locationPredicate = [NSPredicate predicateWithFormat:@"Location IN %@", locationList];

 NSPredicate *typePredicate = [NSPredicate predicateWithFormat:@"Type IN %@", typeList];

 NSPredicate *notePredicate = [NSPredicate predicateWithFormat:@"Note contains[c] %@", @"Some Text"];

 NSPredicate *startDatePredicate = [NSPredicate predicateWithFormat:@"Date => @", fromDate];

 NSPredicate *endDatePredicate = [NSPredicate predicateWithFormat:@"Date <= @", toDate];

Now you just need to join them into just one predicate: Apple's documentation states:

You should structure compound predicates to minimize the amount of work done. Regular expression matching in particular is an expensive operation. In a compound predicate, you should therefore perform simple tests before a regular expression;

This being said then you should start with the "easy" predicates first. So:

NSCompoundPredicate *compoundPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects: startDatePredicate, endDatePredicate, inCategoryPredicate, locationPredicate, typePredicate, notePredicate];

You can always get an idea of what the predicate (sql where) looks like if you NSLog it.