Nspredicate Cheat Sheet (Page 2 of 2) in pdf

Tips, Tricks, & Examples

Quick tips

Common mistakes

CFStringTransform normalizes strings if diacritic insensitive isn’t

Using stringWithFormat: to build predicates, prone to have weird

enough. For example you could turn Japanese characters into a

non escaped diacritic characters and artifacts like an apostrophe.

Latin alphabetic representation. It’s extremely powerful with a lot

Use NSPredicate predicateWithFormat instead.

of methods that you can see here:

Using OR OR OR instead of IN, results in repeatable code and can

cfstringtransform/

be less efficient

Make sure your columns are indexed to improve performance of

using IN operators

When using REGEX and Matches, make sure they are the last part

of your predicate statment so it does less work.

[c] case insensitive: lower & uppercase values are treated the

same

[d] diacritic insensitive: special characters treated as the base

Using SELF

character

predicateWithFormat: @"name CONTAINS[c] ' f ' "

When using a predicate on an array, SELF refers to each object in

the array. Here’s an example: Imagine you are a landlord figuring

out which apartments have to pay their water bill. If you have a

Keypath collection queries

list of all the city wide apartment’s that still need to pay called

addressesThatOweWaterBill, we can check that against our

Keypath collection queries work best when you work with a lot of

owned apartments, myApartmentAddresses.

numbers. Being able to easily call the min or max, adding things

NSPredicate *billingPredicate = [NSPredicate

up, and then filtering results can be much simpler when you only

predicateWithFormat: @"SELF IN %@",

have to append an extra parameter. By having an array of

addressesThatOweWaterBill]

expenses, you can easily do a quick check on if something is

below or above a range of allowed expenses.

NSArray *myApartmentsThatOweWaterBill =

[myApartmentAddresses

predicateWithFormat: @"expenses.@avg.doubleValue < 200"

filteredArrayUsingPredicate:billingPredicate]

How Subqueries work

LIKE wildcard match with * and ?

SUBQUERY(collection, variableName, predicate)

* matches 0 or more characters. For example:

Let’s say we have an array of names we want to filter

A subquery takes a collection then iterates through each object

(as variableName) checking the predicate against that object

@["Sarah", "Silva", "silva", "Silvy", "Silvia", Si*"]

(variableName). It works well if you have a collection (A) objects,

[NSPredicate predicateWithFormat: @"SELF ==

and each object has a collection (B) other objects. If you’re trying

%@", "Sarah"]

to filter A based on 2 or more varying attributes of B.

Will return “Sarah”

[NSPredicate predicateWithFormat: @"SUBQUERY(tasks,

[NSPredicate predicateWithFormat: @"SELF LIKE[c]

$task, $task.completionDate != nil AND $task.user =

%@", "Si*"]

'Alex').@count > 0"]

Will return “Silva”, “silva”, “Silvy”, “Silvia”, “Si*”

SUBQUERY(…) returns an array. We need to check if its count > 0

to return the true or false the predicate expects.

? matches 1 character only

[NSPredicate predicateWithFormat: @"SELF LIKE[c] %@",

"Silv?"]

Will return “Silva”, “silva”, “Silvy”

Nspredicate Cheat Sheet Page 2

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