A library of extended scalars for graphql-java
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Extended Scalars for graphql-java

This library provides extended scalars for graphql-java

Scalars in graphql are the leaf nodes of a query, the non compound values that cant be queried further via sub field selections.

The graphql standard specifies that the String, Int, Float, Boolean and ID scalars must be present in a graphql type system but after that it is up to an implementation about what custom scalars are present.

You would use custom scalars when you want to describe more meaningful behavior or ranges of values.

To use this library put the following into your gradle config

compile 'com.graphql-java:graphql-java-extended-scalars:1.0'

or the following into your Maven config

<dependency>
  <groupId>com.graphql-java</groupId>
  <artifactId>graphql-java-extended-scalars</artifactId>
  <version>1.0</version>
</dependency>

Then register the scalar with graphql-java

RuntimeWiring.newRuntimeWiring().scalar(ExtendedScalars.DateTime)

And use it in your schema

scalar DateTime
type Something {
    someDateTime: DateTime
}

DateTime Scalars

  • DateTime
    • An RFC-3339 compliant date time scalar that accepts string values like 1996-12-19T16:39:57-08:00 and produces java.time.OffsetDateTime objects at runtime
  • Time
    • An RFC-3339 compliant time scalar that accepts string values like 16:39:57-08:00 and produces java.time.LocalDate objects at runtime
  • Date
    • An RFC-3339 compliant date scalar that accepts string values like 1996-12-19 and produces java.time.LocalDate objects at runtime

See the rfc3339 spec for more details on the format.

An example declaration in SDL might be:

    type Customer {
        birthDay : Date
        workStartTime : Time
        bornAt : DateTime
    }
    
    type Query {
        customers(bornAfter : DateTime) : [Customers]
    }
    

And example query might look like:

    
    query {
        customers(bornAfter : "1996-12-19T16:39:57-08:00") {
            birthDay
            bornAt
        }
    }
    

Object / Json Scalars

  • Object

    • An object scalar that accepts any object as a scalar value
  • Json

    • A synonym for the Object scalar, it will accept any object as a scalar value

One of the design goals of graphql, is that the type system describes the shape of the data returned.

The Object / Json scalars work against this some what because they can return compound values outside the type system. As such they should be used sparingly. In general your should aim to describe the data via the graphql type system where you can and only resort to the Object / Json scalars in very rare circumstances.

An example might be an extensible graphql system where systems can input custom metadata objects that cant be known at schema type design time.

An example declaration in SDL might be:

    type Customer {
        name : String
        associatedMetaData : Json
    }
    
    type Query {
        customers(filterSyntax : Json) : [Customers]
    }
    

And example query might look like:

    
    query {
        customers(filterSyntax : {
                startSpan : "First",
                matchCriteria : {
                    countryCode : "AU",
                    isoCodes : ["27B-34R", "95A-E23"],
                    
                }
            }) {
            name
            associatedMetaData    
        }
    }
    

Note : The Json scalar is a simple alias type to the Object scalar because often the returned data is a blob of JSON. They are all just objects at runtime in graphql-java terms and what network serialisation protocol is up to you. Choose whichever name you think adds more semantic readers to your schema consumers.

Numeric Scalars

  • PositiveInt
    • An Int scalar that MUST be greater than zero
  • NegativeInt
    • An Int scalar that MUST be less than zero
  • NonPositiveInt
    • An Int scalar that MUST be less than or equal to zero
  • NonNegativeInt
    • An Int scalar that MUST be greater than or equal to zero
  • PositiveFloat
    • An Float scalar that MUST be greater than zero
  • NegativeFloat
    • An Float scalar that MUST be less than zero
  • NonPositiveFloat
    • An Float scalar that MUST be less than or equal to zero
  • NonNegativeFloat
    • An Float scalar that MUST be greater than or equal to zero

The numeric scalars are derivations of the standard graphql Int and Float scalars that enforce range limits.

An example declaration in SDL might be:

    type Customer {
        name : String
        currentHeight : PositiveInt
        weightLossGoal : NonPositiveInt
        averageWeightLoss : NegativeFloat
    }
    
    type Query {
        customers(height : PositiveInt) : [Customers]
    }
    

And example query might look like:

    
    query {
        customers(height : 182) {
            name
            height
            weightLossGoal    
        }
    }
    

Regex Scalars

The RegexScalar has a builder where you provide one or more regex patterns that control the acceptable values for a new scalar.

You name the scalar and it provides an implementation.

For example, imagine a phoneNumber scalar like this :

    RegexScalar phoneNumberScalar = ExtendedScalars.newRegexScalar("phoneNumber")
            .addPattern(Pattern.compile("\\([0-9]*\\)[0-9]*"))
            .build()

Alias Scalars

You can create aliases for existing scalars to add more semantic meaning to them.

For example a link to a social media post could be representing by a String but the name SocialMediaLink is a more semantically meaningful name for that scalar type.

For example, you would build it like this:

    AliasedScalar socialMediaLink = ExtendedScalars.newAliasedScalar("SocialMediaLink")
            .aliasedScalar(Scalars.GraphQLString)
            .build()

And use it in a SDL schema like this :

     type Customer {
           name : String
           socialMediaLink : SocialMediaLink
     }

Note: A future version of the graphql specification may add this capability but in the meantime you can use this facility.

Other Scalars

  • Url
    • An url scalar that accepts string values like https://www.w3.org/Addressing/URL/url-spec.txt and produces java.net.URL objects at runtime