graphql.schema

Class PropertyDataFetcher<T>

java.lang.Object

graphql.schema.PropertyDataFetcher<T>

All Implemented Interfaces:

DataFetcher<T>, TrivialDataFetcher<T>

@PublicApi
public class PropertyDataFetcher<T>
extends java.lang.Object
implements DataFetcher<T>, TrivialDataFetcher<T>

This is the default data fetcher used in graphql-java. It will examine maps and POJO java beans for values that match the desired name, typically the field name or it will use a provided function to obtain values. maps and POJO java beans for values that match the desired name.

It uses the following strategies

• If the source is null, return null
• If the source is a Map, return map.get(propertyName)
• If a function is provided, it is used
• Find a public JavaBean getter method named `propertyName`
• Find any getter method named `propertyName` and call method.setAccessible(true)
• Find a public field named `propertyName`
• Find any field named `propertyName` and call field.setAccessible(true)
• If this cant find anything, then null is returned

You can write your own data fetchers to get data from some other backing system if you need highly customised behaviour.

See Also:

DataFetcher

Constructor Summary

Constructors

Constructor and Description
PropertyDataFetcher(java.lang.String propertyName) This constructor will use the property name and examine the DataFetchingEnvironment.getSource() object for a getter method or field with that name.

Method Summary

Modifier and Type	Method and Description
static void	clearReflectionCache() PropertyDataFetcher caches the methods and fields that map from a class to a property for runtime performance reasons as well as negative misses.
static <T,O> PropertyDataFetcher<T>	fetching(java.util.function.Function<O,T> function) Returns a data fetcher that will present the DataFetchingEnvironment.getSource() object to the supplied function to obtain a value, which allows you to use Java 8 method references say obtain values in a more type safe way.
static <T> PropertyDataFetcher<T>	fetching(java.lang.String propertyName) Returns a data fetcher that will use the property name to examine the DataFetchingEnvironment.getSource() object for a getter method or field with that name, or if its a map, it will look up a value using property name as a key.
T	get(DataFetchingEnvironment environment) This is called by the graphql engine to fetch the value.
java.lang.String	getPropertyName()
static boolean	setUseNegativeCache(boolean flag) This can be used to control whether PropertyDataFetcher will cache negative lookups for a property for performance reasons.
static boolean	setUseSetAccessible(boolean flag) This can be used to control whether PropertyDataFetcher will use AccessibleObject.setAccessible(boolean) to gain access to property values.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PropertyDataFetcher

public PropertyDataFetcher(java.lang.String propertyName)

This constructor will use the property name and examine the DataFetchingEnvironment.getSource() object for a getter method or field with that name.

Parameters:

propertyName - the name of the property to retrieve

Method Detail

fetching

public static <T> PropertyDataFetcher<T> fetching(java.lang.String propertyName)

Returns a data fetcher that will use the property name to examine the DataFetchingEnvironment.getSource() object for a getter method or field with that name, or if its a map, it will look up a value using property name as a key.

For example :

 

      DataFetcher functionDataFetcher = fetching("pojoPropertyName");

 
 

Type Parameters:

T - the type of result

Parameters:

propertyName - the name of the property to retrieve

Returns:

a new PropertyDataFetcher using the provided function as its source of values

fetching

public static <T,O> PropertyDataFetcher<T> fetching(java.util.function.Function<O,T> function)

Returns a data fetcher that will present the DataFetchingEnvironment.getSource() object to the supplied function to obtain a value, which allows you to use Java 8 method references say obtain values in a more type safe way.

For example :

 

      DataFetcher functionDataFetcher = fetching(Thing::getId);

 
 

Type Parameters:

O - the type of the source object

T - the type of result

Parameters:

function - the function to use to obtain a value from the source object

Returns:

a new PropertyDataFetcher using the provided function as its source of values

getPropertyName

public java.lang.String getPropertyName()

Returns:

the property that this is fetching for

get

public T get(DataFetchingEnvironment environment)

Description copied from interface: DataFetcher

This is called by the graphql engine to fetch the value. The DataFetchingEnvironment is a composite context object that tells you all you need to know about how to fetch a data value in graphql type terms.

Specified by:

get in interface DataFetcher<T>

Parameters:

environment - this is the data fetching environment which contains all the context you need to fetch a value

Returns:

a value of type T. May be wrapped in a DataFetcherResult

clearReflectionCache

public static void clearReflectionCache()

PropertyDataFetcher caches the methods and fields that map from a class to a property for runtime performance reasons as well as negative misses.

However during development you might be using an assistance tool like JRebel to allow you to tweak your code base and this caching may interfere with this. So you can call this method to clear the cache. A JRebel plugin could be developed to do just that.

setUseSetAccessible

public static boolean setUseSetAccessible(boolean flag)

This can be used to control whether PropertyDataFetcher will use AccessibleObject.setAccessible(boolean) to gain access to property values. By default it PropertyDataFetcher WILL use setAccessible.

Parameters:

flag - whether to use setAccessible

Returns:

the previous value of the flag

setUseNegativeCache

public static boolean setUseNegativeCache(boolean flag)

This can be used to control whether PropertyDataFetcher will cache negative lookups for a property for performance reasons. By default it PropertyDataFetcher WILL cache misses.

Parameters:

flag - whether to cache misses

Returns:

the previous value of the flag