graphql.schema

Interface Coercing<I,O>

All Known Implementing Classes:

GraphqlBooleanCoercing, GraphqlFloatCoercing, GraphqlIDCoercing, GraphqlIntCoercing, GraphqlStringCoercing

@PublicSpi
public interface Coercing<I,O>

The Coercing interface is used by GraphQLScalarTypes to parse and serialise object values.

There are two major responsibilities, result coercion and input coercion.

Result coercion is taking a value from a Java object and coercing it into the constraints of the scalar type. For example imagine a DateTime scalar, the result coercion would need to take an object and turn it into a ISO date or throw an exception if it cant.

Input coercion is made out of three different methods parseLiteral(Object) which converts an literal Ast into an internal input value, parseValue(Object) which converts an external input value into an internal one and valueToLiteral(Object) which is a translation between an external input value into a literal.
The relationship between these three methods is as follows: It is required that every valid external input values for parseValue(Object) is also valid for valueToLiteral(Object) and vice versa. Furthermore the literals returned by valueToLiteral(Object) are required to be valid for parseLiteral(Object).

Method Summary

Modifier and Type	Method and Description
I	parseLiteral(@NotNull java.lang.Object input) Called during query validation to convert a query input AST node into a Java object acceptable for the scalar type.
default I	parseLiteral(java.lang.Object input, java.util.Map<java.lang.String,java.lang.Object> variables) Called during query execution to convert a query input AST node into a Java object acceptable for the scalar type.
I	parseValue(@NotNull java.lang.Object input) Called to resolve an input from a query variable into a Java object acceptable for the scalar type.
O	serialize(@NotNull java.lang.Object dataFetcherResult) Called to convert a Java object result of a DataFetcher to a valid runtime value for the scalar type.
default @NotNull Value	valueToLiteral(@NotNull java.lang.Object input) Converts an external input value to a literal (Ast Value).

Method Detail

serialize

O serialize(@NotNull
            @NotNull java.lang.Object dataFetcherResult)
     throws CoercingSerializeException

Called to convert a Java object result of a DataFetcher to a valid runtime value for the scalar type.

Note : Throw CoercingSerializeException if there is fundamental problem during serialisation, don't return null to indicate failure.

Note : You should not allow RuntimeExceptions to come out of your serialize method, but rather catch them and fire them as CoercingSerializeException instead as per the method contract.

Parameters:

dataFetcherResult - is never null

Returns:

a serialized value which may be null.

Throws:

CoercingSerializeException - if value input can't be serialized

parseValue

@NotNull
I parseValue(@NotNull
                      @NotNull java.lang.Object input)
               throws CoercingParseValueException

Called to resolve an input from a query variable into a Java object acceptable for the scalar type.

Note : You should not allow RuntimeExceptions to come out of your parseValue method, but rather catch them and fire them as CoercingParseValueException instead as per the method contract.

Parameters:

input - is never null

Returns:

a parsed value which is never null

Throws:

CoercingParseValueException - if value input can't be parsed

parseLiteral

@NotNull
I parseLiteral(@NotNull
                        @NotNull java.lang.Object input)
                 throws CoercingParseLiteralException

Called during query validation to convert a query input AST node into a Java object acceptable for the scalar type. The input object will be an instance of Value.

Note : You should not allow RuntimeExceptions to come out of your parseLiteral method, but rather catch them and fire them as CoercingParseLiteralException instead as per the method contract.

Parameters:

input - is never null

Returns:

a parsed value which is never null

Throws:

CoercingParseLiteralException - if input literal can't be parsed

parseLiteral

@NotNull
default I parseLiteral(java.lang.Object input,
                                java.util.Map<java.lang.String,java.lang.Object> variables)
                         throws CoercingParseLiteralException

Called during query execution to convert a query input AST node into a Java object acceptable for the scalar type. The input object will be an instance of Value.

Note : You should not allow RuntimeExceptions to come out of your parseLiteral method, but rather catch them and fire them as CoercingParseLiteralException instead as per the method contract.

Many scalar types don't need to implement this method because they don't take AST VariableReference objects and convert them into actual values. But for those scalar types that want to do this, then this method should be implemented.

Parameters:

input - is never null

variables - the resolved variables passed to the query

Returns:

a parsed value which is never null

Throws:

CoercingParseLiteralException - if input literal can't be parsed

valueToLiteral

@NotNull
default @NotNull Value valueToLiteral(@NotNull
                                               @NotNull java.lang.Object input)

Converts an external input value to a literal (Ast Value). IMPORTANT: the argument is validated before by calling parseValue(Object).

Parameters:

input - an external input value

Returns:

The literal matching the external input value.