Package com.daml.ledger.javaapi.data.codegen

Interface ValueDecoder<Data>

Type Parameters:
Data - The codegen or primitive type that this decodes a Value to.
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface ValueDecoder<Data>
A converter from the encoded form of a Daml value, represented by Value, to the codegen-decoded form, represented by Data.

Every codegen class for a template, record, or variant includes a valueDecoder method that produces one of these. If the data type has type parameters, valueDecoder has arguments that correspond to ValueDecoders for those type arguments. For primitive types that are not code-generated, see PrimitiveValueDecoders. 

 // given template 'Foo', and encoded payload 'Value fooValue'
 Foo foo = Foo.valueDecoder().decode(fooValue);

 // given Daml datatypes 'Bar a b' and 'Baz',
 // and encoded 'Bar' 'Value barValue'
 Bar<Baz, Long> bar = Bar.valueDecoder(
     Baz.valueDecoder(), PrimitiveValueDecoders.fromInt64)
   .decode(barValue);

 Bar<List<Baz>, Map<Long, String>> barWithAggregates = Bar.valueDecoder(
     PrimitiveValueDecoders.fromList(Baz.valueDecoder),
     PrimitiveValueDecoders.fromGenMap(
       PrimitiveValueDecoders.fromInt64,
       PrimitiveValueDecoders.fromText))
   .decode(barAggregateValue);
There is also a decode(Value, UnknownTrailingFieldPolicy) method that takes an additional UnknownTrailingFieldPolicy This method is used to handle unknown trailing fields in the value. Currently, the error is thrown if there are unknown trailing fields or extra fields are ignored.

In the following situation if the following DAML data object is defined in the DAML project on the client side: 

 data Bar = Bar { bar : Int, baz: Int } deriving (Eq, Show)
And the following value is received from the ledger: 
 Value(1, 2, Optional(3))
if the following code is executed on the client side, the IllegalArgumentException is thrown: 
     Bar bar = Bar.valueDecoder().decode(value, UnknownTrailingFieldPolicy.STRICT);
and if the following code is executed on the client side, the Bar object is created with bar = 1 and baz = 2, while the extra field 3 is ignored: 
     Bar bar = Bar.valueDecoder().decode(value, UnknownTrailingFieldPolicy.IGNORE);

  • Method Summary

    Modifier and Type
    Method
    Description
    Data
    decode(Value value)
    Method used to decode value with default policy (STRICT) to handle unknown trailing fields
    default Data
    decode(Value value, UnknownTrailingFieldPolicy policy)