Package org.instancio

Interface BaseApi<T>

Type Parameters:

T - the type of object to create

All Known Subinterfaces:

InstancioApi<T>, InstancioCartesianProductApi<T>, InstancioClassApi<T>, InstancioCollectionsApi<C>

interface BaseApi<T>

Defines top-level operations supported by the API.

Since:

4.0.0

Method Summary

Modifier and Type	Method	Description
BaseApi<T>	applyFeed(TargetSelector selector, Feed feed)	Applies the provided feed to the specified selector.
BaseApi<T>	applyFeed(TargetSelector selector, FeedProvider provider)	Creates a feed and applies it to the specified selector.
BaseApi<T>	assign(Assignment... assignments)	Generates values based on given assignments.
<V> BaseApi<T>	filter(TargetSelector selector, FilterPredicate<V> predicate)	Filters generated values using given predicate.
<V> BaseApi<T>	generate(TargetSelector selector, GeneratorSpec<V> spec)	Customises values using arbitrary generator specs.
<V> BaseApi<T>	generate(TargetSelector selector, GeneratorSpecProvider<V> gen)	Customises values using built-in generators provided by the gen parameter, of type Generators.
BaseApi<T>	ignore(TargetSelector selector)	Specifies that a class or field should be ignored.
<V> BaseApi<T>	onComplete(TargetSelector selector, OnCompleteCallback<V> callback)	A callback that gets invoked after the root object has been fully populated.
<V> BaseApi<T>	set(TargetSelector selector, V value)	Sets a value to matching selector targets.
BaseApi<T>	setBlank(TargetSelector selector)	Specifies that a blank object should be generated for the selected target.
<V> BaseApi<T>	setModel(TargetSelector selector, Model<V> model)	Applies given model to the specified selector.
BaseApi<T>	subtype(TargetSelector selector, Class<?> subtype)	Maps target field or class to the given subtype.
<V> BaseApi<T>	supply(TargetSelector selector, Supplier<V> supplier)	Supplies an object using a Supplier.
<V> BaseApi<T>	supply(TargetSelector selector, Generator<V> generator)	Supplies an object using a Generator to matching selector targets.
BaseApi<T>	withMaxDepth(int maxDepth)	Specifies the maximum depth for populating an object.
BaseApi<T>	withNullable(TargetSelector selector)	Specifies that a field or class is nullable.
BaseApi<T>	withSeed(long seed)	Sets the seed value for the random number generator.
BaseApi<T>	withUnique(TargetSelector selector)	Specifies that the given selector's target(s) should have unique values.

Method Details

ignore

BaseApi<T> ignore(TargetSelector selector)

Specifies that a class or field should be ignored.

Example:

 Person person = Instancio.of(Person.class)
     .ignore(field(Phone::getPhoneNumber))
     .ignore(allStrings())
     .create();
 

will create a fully populated person, but will ignore the getPhoneNumber field, and all strings.

Precedence

This method has higher precedence than other API methods. Once a target is ignored, no other selectors will apply. For example, the following snippet will trigger an unused selector error because field(Phone::getNumber) is redundant:

 Person person = Instancio.of(Person.class)
     .ignore(all(Phone.class))
     .set(field(Phone::getNumber), "123-45-56")
     .create();
 

Usage with Java records

If ignore() targets one of the required arguments of a record constructor, then a default value for the ignored type will be generated.

Example:

 record PersonRecord(String name, int age) {}

 PersonRecord person = Instancio.of(PersonRecord.class)
     .ignore(allInts())
     .ignore(allStrings())
     .create();

 // will produce: PersonRecord[name=null, age=0]
 

Parameters:

selector - for fields and/or classes this method should be applied to

Returns:

API builder reference

Since:

4.0.0

withNullable

BaseApi<T> withNullable(TargetSelector selector)

Specifies that a field or class is nullable. By default, Instancio assigns non-null values to fields. If marked as nullable, Instancio will generate either a null or non-null value.

Example:

 Person person = Instancio.of(Person.class)
     .withNullable(allStrings())
     .withNullable(field(Person::getAddress))
     .withNullable(fields().named("lastModified"))
     .create();
 

Note: a type marked as nullable using this method is only nullable when declared as a field, but not as a collection element, or map key/value. For example, withNullable(allStrings()) will not generate nulls in a List<String>.

Parameters:

selector - for fields and/or classes this method should be applied to

Returns:

API builder reference

set

<V> BaseApi<T> set(TargetSelector selector,
 V value)

Sets a value to matching selector targets.

Example: if Person class contains a List<Phone>, the following snippet will set all the country code of all phone instances to "+1".

 Person person = Instancio.of(Person.class)
     .set(field(Phone::getCountryCode), "+1")
     .create();
 

Note: Instancio will not

• populate or modify objects supplied by this method
• apply other set(), supply(), or generate()} methods with matching selectors to the supplied object
• invoke onComplete() callbacks on supplied instances

Type Parameters:

V - type of the value

Parameters:

selector - for fields and/or classes this method should be applied to

value - value to set

Returns:

API builder reference

Since:

4.0.0

See Also:

• supply(TargetSelector, Supplier)

setModel

@ExperimentalApi
<V> BaseApi<T> setModel(TargetSelector selector,
 Model<V> model)

Applies given model to the specified selector.

For example, given the following classes and Model:

 record Foo(String value) {}
 record Container(Foo fooA, Foo fooB) {}

 Model<Foo> fooModel = Instancio.of(Foo.class)
     .set(field(Foo::value), "foo")
     .toModel();
 

The model can be applied to a specific Foo field declared by the Container:

 Container container = Instancio.of(Container.class)
     .setModel(field(Container::fooA), fooModel)
     .create();
 

Alternatively, to apply the model to all instances of Foo:

 Container container = Instancio.of(Container.class)
     .setModel(all(Foo.class), fooModel)
     .create();
 

Note: the following properties of the supplied model are not applied to the target object:

• Settings
• lenient() mode
• custom seed value

See the user guide for further details.

Type Parameters:

V - the type of object this model represents

Parameters:

selector - to which the model will be applied to

model - to apply to the given selector's target

Returns:

API builder reference

Since:

4.4.0

supply

<V> BaseApi<T> supply(TargetSelector selector,
 Supplier<V> supplier)

Supplies an object using a Supplier.

Example:

 Person person = Instancio.of(Person.class)
     .supply(all(LocalDateTime.class), () -> LocalDateTime.now())
     .supply(field(Address::getPhoneNumbers), () -> List.of(
         new PhoneNumber("+1", "123-45-67"),
         new PhoneNumber("+1", "345-67-89")))
     .create();
 

Note: Instancio will not

• populate or modify objects supplied by this method
• apply other set(), supply(), or generate()} methods with matching selectors to the supplied object
• invoke onComplete() callbacks on supplied instances

If you require the supplied object to be populated and/or selectors to be applied, use the supply(TargetSelector, Generator) method instead.

Type Parameters:

V - type of the supplied value

Parameters:

selector - for fields and/or classes this method should be applied to

supplier - providing the value for given selector

Returns:

API builder reference

Since:

4.0.0

See Also:

• supply(TargetSelector, Generator)

supply

<V> BaseApi<T> supply(TargetSelector selector,
 Generator<V> generator)

Supplies an object using a Generator to matching selector targets. By default, Instancio will populate uninitialised fields of the supplied object. This includes fields with null or default primitive values.

This method supports the following use cases.

Generate random objects

This method provides an instance of Random that can be used to randomise generated objects. For example, if Instancio did not support creation of java.time.Year, it could be generated as follows:

 List<Year> years = Instancio.ofList(Year.class)
     .supply(all(Year.class), random -> Year.of(random.intRange(1900, 2000)))
     .create();
 

Provide a partially initialised instance

In some cases, an object may need to be created in a certain state or instantiated using a specific constructor to be in a valid state. A partially initialised instance can be supplied using this method, and Instancio will populate remaining fields that are null:

 Person person = Instancio.of(Person.class)
     .supply(field(Person::getAddress), random -> new Address("Springfield", "USA"))
     .create();
 

This behaviour is controlled by the AfterGenerate hint specified by Generator.hints(). Refer to the Generator.hints() Javadoc for details, or Custom Generators section of the user guide.

Type Parameters:

V - type of the value to generate

Parameters:

selector - for fields and/or classes this method should be applied to

generator - that will provide the values

Returns:

API builder reference

Since:

4.0.0

See Also:

• Generator
• AfterGenerate
• Keys.AFTER_GENERATE_HINT

generate

<V> BaseApi<T> generate(TargetSelector selector,
 GeneratorSpecProvider<V> gen)

Customises values using built-in generators provided by the gen parameter, of type Generators.

Example:

 Person person = Instancio.of(Person.class)
     .generate(field(Person::getAge), gen -> gen.ints().range(18, 100))
     .generate(all(LocalDate.class), gen -> gen.temporal().localDate().past())
     .generate(field(Address::getPhoneNumbers), gen -> gen.collection().size(5))
     .generate(field(Address::getCity), gen -> gen.oneOf("Burnaby", "Vancouver", "Richmond"))
     .create();
 

Type Parameters:

V - type of object to generate

Parameters:

selector - for fields and/or classes this method should be applied to

gen - provider of customisable built-in generators (also known as specs)

Returns:

API builder reference

See Also:

• generate(TargetSelector, GeneratorSpec)
• Generators

generate

<V> BaseApi<T> generate(TargetSelector selector,
 GeneratorSpec<V> spec)

Customises values using arbitrary generator specs.

Example:

 Person person = Instancio.of(Person.class)
     .generate(field(Person::getAge), Instancio.ints().range(18, 100))
     .generate(all(LocalDate.class),  Instancio.temporal().localDate().past())
     .generate(field(Phone::getNumber),  MyCustomGenerators.phones().northAmerican())
     .create();
 

Type Parameters:

V - type of object to generate

Parameters:

selector - for fields and/or classes this method should be applied to

spec - generator spec

Returns:

API builder reference

Since:

4.0.0

See Also:

• generate(TargetSelector, GeneratorSpecProvider)

onComplete

<V> BaseApi<T> onComplete(TargetSelector selector,
 OnCompleteCallback<V> callback)

A callback that gets invoked after the root object has been fully populated.

Example:

 // Sets countryCode field on all instances of Phone to the specified value
 Person person = Instancio.of(Person.class)
     .onComplete(all(Phone.class), (Phone phone) -> phone.setCountryCode("+1"))
     .create();
 

Note: callbacks are never invoked on objects provided using:

• set(TargetSelector, Object)
• supply(TargetSelector, Supplier)

 OnCompleteCallback<String> callback = (String value) -> {
     // do something with the value
 };

 Person person = Instancio.of(Person.class)
     .set(field(Phone::getCountryCode), "+1")
      // The callback will not be invoked because
      // Phone.countryCode value was provided via set() method
     .onComplete(field(Phone::getCountryCode), callback)
     .create();
 

Type Parameters:

V - type of object handled by the callback

Parameters:

selector - for fields and/or classes this method should be applied to

callback - to invoke after object has been populated

Returns:

API builder reference

Since:

4.0.0

filter

@ExperimentalApi
<V> BaseApi<T> filter(TargetSelector selector,
 FilterPredicate<V> predicate)

Filters generated values using given predicate. If a value is rejected, a new value will be generated, which will also be tested against the predicate. If no value is accepted after Keys.MAX_GENERATION_ATTEMPTS, an exception will be thrown.

A simple example is to generate a list of even numbers:

 List<Integer> evenNumbers = Instancio.ofList(Integer.class)
     .filter(allInts(), (Integer i) -> i % 2 == 0)
     .create();
 

Note that customising objects using this method is less efficient than generate(TargetSelector, GeneratorSpecProvider). The latter should be preferred where possible.

Type Parameters:

V - the type of object the predicate is evaluated against

Parameters:

selector - for fields and/or classes this method should be applied to

predicate - that must be satisfied by the generated value

Returns:

API builder reference

Since:

4.6.0

See Also:

• Keys.MAX_GENERATION_ATTEMPTS

subtype

BaseApi<T> subtype(TargetSelector selector,
 Class<?> subtype)

Maps target field or class to the given subtype. This can be used in the following cases:

1. to specify an implementation for interfaces or abstract classes
2. to override default implementations used by Instancio

Specify an implementation for an abstract type

When Instancio encounters an interface or an abstract type it is not aware of (for example, that is not part of the JDK), it will not be able to instantiate it. This method can be used to specify an implementation to use in such cases. For example:

 WidgetContainer container = Instancio.of(WidgetContainer.class)
     .subtype(all(AbstractWidget.class), ConcreteWidget.class)
     .create();
 

Override default implementations

By default, Instancio uses certain defaults for collection classes, for example ArrayList for List. If an alternative implementation is required, this method allows to specify it:

 Person person = Instancio.of(Person.class)
     .subtype(all(List.class), LinkedList.class)
     .create();
 

will use the LinkedList implementation for all Lists.

Parameters:

selector - for fields and/or classes this method should be applied to

subtype - to map the selector to

Returns:

API builder reference

Since:

4.0.0

assign

BaseApi<T> assign(Assignment... assignments)

Generates values based on given assignments. An Assignment can be created using one of the builder patterns provided by the Assign class.

• Assign.valueOf(originSelector).to(destinationSelector)
• Assign.given(originSelector).satisfies(predicate).set(destinationSelector, value)
• Assign.given(originSelector, destinationSelector).set(predicate, value)

For example, the following snippet uses Assign.given(TargetSelector, TargetSelector) to create an assignment that sets Phone.countryCode based on the value of the Address.country field:

 Assignment assignment = Assign.given(field(Address::getCountry), field(Phone::getCountryCode))
     .set(When.isIn("Canada", "USA"), "+1")
     .set(When.is("Italy"), "+39")
     .set(When.is("Poland"), "+48")
     .set(When.is("Germany"), "+49");

 Person person = Instancio.of(Person.class)
     .generate(field(Address::getCountry), gen -> gen.oneOf("Canada", "USA", "Italy", "Poland", "Germany"))
     .assign(assignment)
     .create();
 

The above API allows specifying different values for a given origin/destination pair. An alternative for creating a conditional is provided by Assign.given(TargetSelector). This method allows specifying different destination selectors for a given origin:

 Assignment shippedOrderAssignment = Assign.given(Order::getStatus)
     .is(OrderStatus.SHIPPED)
     .supply(field(Order::getDeliveryDueDate), () -> LocalDate.now().plusDays(2));

 Assignment cancelledOrderAssignment = Assign.given(Order::getStatus)
      .is(OrderStatus.CANCELLED)
      .set(field(Order::getCancellationReason), "Shipping delays")
      .generate(field(Order::getCancellationDate), gen -> gen.temporal().instant().past());

 List<Order> orders = Instancio.ofList(Order.class)
     .generate(all(OrderStatus.class), gen -> gen.oneOf(OrderStatus.SHIPPED, OrderStatus.CANCELLED))
     .assign(shippedOrderAssignment, cancelledOrderAssignment)
     .create();
 

Limitations of assignments

Using assignments has a few limitations to be aware of.

• The origin selector must match a single target. It must not be a SelectorGroup created via Select.all(GroupableSelector...) or primitive/wrapper selector, such as Select.allInts()
• An assignment where the origin selector's target is within a collection element must have a destination selector within the same collection element.
• Circular assignments will produce an error.

Parameters:

assignments - one or more assignment expressions for setting values

Returns:

API builder reference

Throws:

InstancioApiException - if the origin selector of an assignment matches more than one target, or the assignments form a cycle

Since:

4.0.0

See Also:

• Assign

applyFeed

@ExperimentalApi
BaseApi<T> applyFeed(TargetSelector selector,
 Feed feed)

Applies the provided feed to the specified selector. The selector targets must be POJOs or Java records. Properties from the feed will be automatically mapped to the selected objects.

For example, we can generate instances of the following record:

 record Person(String firstName, String lastName, String fullName,
               int age, String username, String email) {}
 

using data from a CSV file (formatted for readability):

 firstName, lastName, age, username
 John,      Doe,      24,  john_doe
 Alice,     Smith,    55,  alice_s
 # more entries...
 

by defining the following feed:

 @Feed.Source(resource = "persons.csv")
 interface PersonFeed extends Feed {

     @TemplateSpec("${firstName} ${lastName}")
     FeedSpec<String> fullName();

     @GeneratedSpec(CustomEmailGenerator.class)
     FeedSpec<String> email();
 }
 

and applying the feed using the all(Person.class) selector:

 Feed personFeed = Instancio.createFeed(PersonFeed.class);

 List<Person> persons = Instancio.ofList(Person.class)
     .applyFeed(all(Person.class), personFeed)
     .create();
 

Data from the CSV will be mapped to Person fields by matching field names to property names in the data file.

• Note that PersonFeed does not need to declare firstName() and lastName() methods (they are mapped automatically).
• fullName() and email() can also be mapped to the Person object, even though these are generated and not present in the data file.

Parameters:

selector - for fields and/or classes this method should be applied to

feed - the feed to apply to the selector

Returns:

API builder reference

Since:

5.0.0

See Also:

• Instancio.createFeed(Class)
• applyFeed(TargetSelector, FeedProvider)

applyFeed

@ExperimentalApi
BaseApi<T> applyFeed(TargetSelector selector,
 FeedProvider provider)

Creates a feed and applies it to the specified selector. The selector's target must be a POJO or a Java record. Properties from the feed will be automatically mapped to the selected object.

For example, given the following CSV file (formatted for readability):

 firstName, lastName, age, username
 John,      Doe,      24,  john_doe
 Alice,     Smith,    55,  alice_s
 # more entries...
 

and a record with matching properties:

 class Person(String firstName, String lastName, int age, String username) {}
 

a feed can be applied as follows:

 List<Person> persons = Instancio.ofList(Person.class)
     .applyFeed(all(Person.class), feed -> feed.ofResource("data/persons.csv"))
     .create();

 // Output:
 // [Person[firstName=John, lastName=Doe, age=24, username=john_doe],
 //  Person[firstName=Alice, lastName=Smith, age=55, username=alice_s]]
 

Parameters:

selector - for fields and/or classes this method should be applied to

provider - the provider API for specifying feed configuration

Returns:

API builder reference

Since:

5.0.0

See Also:

• applyFeed(TargetSelector, Feed)

withMaxDepth

BaseApi<T> withMaxDepth(int maxDepth)

Specifies the maximum depth for populating an object. The root object is at depth zero. Children of the root object are at depth 1, grandchildren at depth 2, and so on.

Instancio will populate values up to the maximum depth. Beyond that, values will be null unless the maximum depth is set to a higher value.

The default maximum depth is defined by Keys.MAX_DEPTH.

Note: this method is a shorthand for:

 int maxDepth = 5;
 Person person = Instancio.of(Person.class)
     .withSettings(Settings.create().set(Keys.MAX_DEPTH, maxDepth))
     .create();
 

If the maximum depth is specified using Settings and this method, then this method takes precedence.

Parameters:

maxDepth - the maximum depth, must not be negative

Returns:

API builder reference

Since:

4.0.0

withSeed

BaseApi<T> withSeed(long seed)

Sets the seed value for the random number generator. If the seed is not specified, a random seed will be used. Specifying the seed is useful for reproducing test results. By specifying the seed value, the same random data will be generated again.

Example:

 // Generates a different UUID each time
 UUID result = Instancio.create(UUID.class);

 // Generates the same UUID each time
 UUID result = Instancio.of(UUID.class)
     .withSeed(1234)
     .create();
 

Parameters:

seed - for the random number generator

Returns:

API builder reference

Since:

4.0.0

setBlank

@ExperimentalApi
BaseApi<T> setBlank(TargetSelector selector)

Specifies that a blank object should be generated for the selected target.

A blank object has the following properties:

• value fields (strings, numbers, dates, etc) are null
• arrays, collections, and maps are empty
• nested POJOs are blank

Example:

 Person person = Instancio.of(Person.class)
     .setBlank(field(Person::getAddress))
     .create();

 // Output:
 // Person[
 //   name="GNQTXA",
 //   dateOfBirth=1988-04-09,
 //   address=Address[street=null, city=null, country=null] // blank Address
 //]
 

Parameters:

selector - for fields and/or classes this method should be applied to

Returns:

API builder reference

Since:

4.7.0

See Also:

• Instancio.createBlank(Class)
• Instancio.ofBlank(Class)

withUnique

@ExperimentalApi
BaseApi<T> withUnique(TargetSelector selector)

Specifies that the given selector's target(s) should have unique values.

Example:

 record Data(int foo, int bar) {}

 List<Data> results = Instancio.ofList(Data.class)
     .size(100)
     .withUnique(field(Data::foo))
     .create();
 

The above snippet generates a list of Data instances with unique foo values. Note that values will be unique across all targets that match the selector. For instance, the following usages:

• withUnique(allInts())
• withUnique(all(field(Data::foo), field(Data::bar))

would result in unique values for foo and bar with no overlap (i.e. foo and bar are disjoint). To generate unique values per field (with potential overlap), the withUnique() method must be specified per field:

 List<Data> results = Instancio.ofList(Data.class)
     .size(100)
     .withUnique(field(Data::foo)) // e.g. { 601, 42, 573, ...}
     .withUnique(field(Data::bar)) // e.g. { 888, 251, 42, ...}
     .create();
 

If it is impossible to generate a sufficient number of unique values after a certain number of attempts, an exception will be thrown:

 List<Boolean> results = Instancio.ofList(Boolean.class)
     .size(10) // will fail as it's impossible to generate 10 unique booleans
     .withUnique(allBooleans())
     .create();
 

Parameters:

selector - for fields and/or classes this method should be applied to

Returns:

API builder reference

Since:

4.8.0