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NSPredicate

Overview

The NSPredicate class is used to define logical conditions used to constrain a search either for a fetch or for in-memory filtering.

You use predicates to represent logical conditions, used for describing objects in persistent stores and in-memory filtering of objects. You often create predicates from a format string which is parsed by the class methods on NSPredicate; examples include:

• Simple comparisons, such as grade == "7" or firstName like "Shaffiq"

• Case/diacritic insensitive lookups, such as name contains[cd] "itroen"

• Logical operations, such as (firstName like "Mark") OR (lastName like"Adderley")

You can create predicates for relationships, such as:

• group.name matches "work*"

• ALL children.age > 12

• ANY children.age > 12

You can also create predicates for operations, such as @sum.items.price < 1000.

In general, the order for like and matches predicates is propertyName OPERATOR pattern.

It is also common to create predicates directly—this is more efficient, more (type-)safe, and it avoids localization issues.

You can also create predicates that include variables, so that they can be pre-defined (in a tool) before substituting concrete values at runtime. For predicates that use variables, evaluation is a two step process (see predicateWithSubstitutionVariables and evaluateWithObject).

Tasks

Constructors

• NSPredicate

Creating Predicates

• predicateWithFormat
• predicateWithSubstitutionVariables
• predicateWithValue

Evaluating

• evaluateWithObject

Getting Format Information

• predicateFormat

Static Methods

predicateWithFormat

Returns a new predicate by substituting the values in arguments into predicateFormat in the order they appear, and parsing the result.

public static NSPredicate predicateWithFormat(String predicateFormat, NSArray arguments)

Availability

• Available in Mac OS X v10.4 and later.

predicateWithValue

public static NSPredicate predicateWithValue(boolean value)

Discussion

Returns a predicate that always evaluates to value.

Availability

• Available in Mac OS X v10.4 and later.

Instance Methods

evaluateWithObject

Returns true if object matches the conditions specified by the receiver; otherwise false

public boolean evaluateWithObject(Object object)

Discussion

.

Availability

• Available in Mac OS X v10.4 and later.

predicateFormat

public String predicateFormat()

Discussion

Returns the receiver’s format string.

Availability

• Available in Mac OS X v10.4 and later.

predicateWithSubstitutionVariables

Returns a copy of the receiver with the receiver’s variables substituted by values specified in the substitution variables dictionary.

public NSPredicate predicateWithSubstitutionVariables(NSDictionary variables)

Discussion

The substitution variables dictionary is specified by variables which must contain key-value pairs for all variables in the predicate.

The receiver itself is not modified by this method, so you can reuse it for any number of substitutions.

Availability

• Available in Mac OS X v10.4 and later.

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