gqlex is a powerful library that offers a unique path selection solution for GraphQL, called gqleXPath. With this feature, developers can easily navigate the GraphQL data structure and select the information they need. In addition, the library includes an advanced transformation tool that allows for complex data manipulation.

I embarked on a project that demanded the manipulation of GraphQL documents and the querying of a target service using the manipulated GraphQL.

To achieve this, I realized that I needed to use some of the techniques that I had previously used to deal with JSON and XML.

The simplicity of JSONPath and xPath, along with complementary technologies like XSD, XSLT, and JavaScript, have contributed to the widespread use of XML and JSON over the years. These tools provide developers with extensive capabilities to select and manipulate JSON or XML documents.

GraphQL and JSON are two separate schema files that serve different purposes and are not always used for externalizing or retrieving service data. Unlike JSON, which is primarily used for data storage and exchange, GraphQL documents are used only for sending queries and mutations to the GraphQL service and not for any other purpose, such as data formats like in JSON or XML.

To modify a GraphQL document, the following steps need to be followed:

1. Traverse through the GraphQL document.
2. Identify the relevant GraphQL node or nodes.
3. Manipulate the GraphQL node or nodes as required.
4. Create a new GraphQL document with the manipulated node or nodes.
5. Pass the new GraphQL document to the GraphQL server to execute the query or mutation.

Let's exclude point (5) from our discussion, as it can be accomplished through multiple tools and code snippets.

I found no open-source solution that could traverse the GraphQL document, select the relevant nodes, and manipulate the GraphQL document.

The article discusses the gqlex solution, which provides an intuitive solution for developers who need assistance with,

1. Traverse through the GraphQL document
2. Select nodes in the GraphQL document
3. Manipulate selected nodes in the GraphQL document

The article will,

• Describe the gqlex and abilities
• Play with code
• Elaborate on use cases

gqlex is a Java-based library.

In order to use the library, you should mvn clean install,

Soon, the artifact will be available via artifactory

gqlex leans on the graphql-java under MIT license, provide GraphQL java implementation,

POM file

<dependency>
   <groupId>com.graphql-java</groupId>
   <artifactId>graphql-java</artifactId>
   <version>20.4</version>
</dependency>

Every element in GraphQL, such as document, query, mutation, fragment, inline fragment, directive, etc., is derived from a node with unique attributes and behavior.

gqlex uses the observer pattern pattern where the GraphQL document acts as a subject, traverses the entire document and notifies relevant observers on the node and context.

This observer pattern separates the traversal over the GraphQL document from the execution part that the observer consumer code would like to perform.

XML has XPath. JSON has JSONPath.

And ... GraphQL document has gqleXPath.

gqleXPath can be used to navigate through nodes in a GraphQL document. gqleXPath uses path expressions to select nodes or node on the GraphQL document.

Behind the scenes, the gqleXPath utilizes the traversal module and selects the node according to the required expression.

gqleXPath uses path expressions to select nodes in GraphQL document. The node is selected by following a path or steps.

The most useful path expressions are listed below:

The library also provides an equivalent code named SyntaxPath that provides gqleXPath expression abilities use of code, mainly used by automation code.

##Transformer The transformer provides the ability to transform (Manipulate) GraphQL document simply. The transformer uses the abilities provided by gqlex such as: gqleXPath, SyntaxPath etc.

The gqlex provides the following transform methods:

1. Add Children - Add children node to selected GraphQL node or nodes
2. Add Sibling - Add sibling node to selected GraphQL node or nodes
3. Duplicate - Duplicate selected node by duplication number, multi nodes cannot be duplicated
4. Remove Children - Remove selected nodes or node
5. Update name - Update selected nodes names or node names, for inline fragments, it will update the typeCondition name
6. Update alias value - update field alias value and fragment spread alias value.

Let's start with traversal over the GrqphQL document

Start with creating my observer, let's name it: StringBuilderObserver

The observer will append the GraphQL node to some StringBuilder.

This way, we achieve separation of concern:

• Traverse over the GraphQL document nodes
• Append node values with StringBuilder ....

public class StringBuilderObserver implements TraversalObserver {
    private final List<StringBuilderElem> stringBuilderElems = new ArrayList<>();

    private final boolean isIgnoreCollection = true;
    @Override
    public void updateNodeEntry(Node node, Node parentNode, Context context, ObserverAction observerAction) {

        String  message = "";
        DocumentElementType documentElementType = context.getDocumentElementType();
        switch (documentElementType) {

            case DOCUMENT:
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "Document", documentElementType.name());

                break;

            case DIRECTIVE:
                message = MessageFormat.format("Name : {0} ||  Type : {1}", ((Directive) node).getName(), documentElementType.name());
                break;
            case FIELD:
                Field field = (Field) node;
                message = MessageFormat.format("Name : {0} || Alias : {1} ||  Type : {2}",
                        field.getName(),
                        field.getAlias(),
                        documentElementType.name());
                break;
            case OPERATION_DEFINITION:
                message = MessageFormat.format("Name : {0} ||  Type : {1}",
                        ((OperationDefinition) node).getOperation().toString(), documentElementType.name());
                break;
            case INLINE_FRAGMENT:
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "InlineFragment",
                        documentElementType.name());

                break;
            case FRAGMENT_DEFINITION:
                message = MessageFormat.format("Name : {0} ||  Type : {1}",
                        ((FragmentDefinition) node).getName(), documentElementType.name());

                break;
            case FRAGMENT_SPREAD:
                message = MessageFormat.format("Node : {0} ||  Type : {1}", ((FragmentSpread) node).getName(), documentElementType.name());
                break;
            case VARIABLE_DEFINITION:
                message = MessageFormat.format("Name : {0} || Default Value : {1} ||  Type : {2}",
                        ((VariableDefinition) node).getName(), ((VariableDefinition) node).getDefaultValue(), documentElementType.name());

                break;
            case ARGUMENT:
                message = MessageFormat.format("Name : {0} || Value : {1} ||  Type : {2}",
                        ((Argument) node).getName(),
                        ((Argument) node).getValue(),
                        documentElementType.name());
                break;
            case ARGUMENTS:
                if(isIgnoreCollection) return;
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "Arguments", documentElementType.name());
                break;
            case SELECTION_SET:
                if(isIgnoreCollection) return;
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "SelectionSet", documentElementType.name());
                break;
            case VARIABLE_DEFINITIONS:
                if(isIgnoreCollection) return;
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "VariableDefinitions", documentElementType.name());
                break;
            case DIRECTIVES:
                if(isIgnoreCollection) return;
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "Directives", documentElementType.name());
                break;
            case DEFINITIONS:
                if(isIgnoreCollection) return;
                message = MessageFormat.format("Node : {0} ||  Type : {1}", "Definitions", documentElementType.name());

                break;
        }

        if(Strings.isNullOrEmpty(message)){
            return;
        }

        stringBuilderElems.add(new StringBuilderElem(message, context.getLevel()));

        levels.add(context.getLevel());
        //spaces++;
    }
    private final List<Integer> levels = new ArrayList<>();

    public String getGqlBrowsedPrintedString() {
        return getStringAs(true);
    }

    private String getStringAs(boolean isIdent) {
        int j=0;
        StringBuilder stringBuilder = new StringBuilder();
        for (StringBuilderElem stringBuilderElem : stringBuilderElems) {
            j++;
            String spaceStr = "";
            if( isIdent) {
                for (int i = 0; i < stringBuilderElem.getDepth(); i++) {
                    spaceStr += " ";
                }
                stringBuilder.append(spaceStr + stringBuilderElem.getName() + "\n");
            }else{
                stringBuilder.append( stringBuilderElem.getName() + (j+1<stringBuilderElems.size()? " " : "") );
            }
        }
        return stringBuilder.toString();
    }

    public String getGqlBrowsedString(){
        return getStringAs(false);
    }

//    int spaces = 0;
    @Override
    public void updateNodeExit( Node node,Node parentNode, Context context, ObserverAction observerAction) {
    }
}

GqlTraversal traversal = new GqlTraversal();

StringBuilderObserver gqlStringBuilderObserver = new StringBuilderObserver();

traversal.getGqlTraversalObservable().addObserver(gqlStringBuilderObserver);
traversal.traverse(file);

System.out.println( gqlStringBuilderObserver.getGqlBrowsedString());

After we saw how the traversal is working, lets digg with some example of gqleXPath selection GraphQL nodes

gqleXPath define an expression language as defined above, in addition the expression language contains more terms to familiar with, Element Name and types abbreviations. Why its important, GraphQL document is more than structure that similar to JSON, GraphQL also provide a DSL that exposed by the GraphQL server and GraphQL language. the types and the element name will assist the gqleXPath to select the exact node or nodes.

Element Names

Available types and abbreviation

Let's practice the gqleXPath expression,

GraphQL Document

In this document, we have 2 node named: 'name', but of different types: argument and field.

query {
    Instrument(Name: "1234") {
        Reference {
            Name
            title
        }
    }
}

• Select all nodes (double slash) 'name' which is an argument type //query/Instrument/name[type=arg]

• Select first node (single slash) 'name' which is an argument type /query/Instrument/name[type=arg]

• //query/.../name[type=arg] Same as query //query/Instrument/name[type=arg]

• Select of 'name' node which is field under Reference, reside under Instrument, reside under query //query/Instrument/Reference/name

• //query/Instrument/.../name Same as //query/Instrument/Reference/name

• //.../name Same as //query/Instrument/Reference/name

GraphQl Document

query Hero($episode: Episode, $withFriends: Boolean!) {
  hero(episode: $episode) {
    name
    friends @include(if: $withFriends) {
      name
    }
    friends @include(if: $withFriends) {
      name
    }
    friends @include(if: $withFriends) {
      name
    }
    friends @include(if: $withFriends) {
      name
    }
  }
}

• Select all query nodes named hero //query[name=hero]

• Select first query (single slash) node named hero /query[name=hero]

• Select all nodes named 'name', reside under friends node //query[name=hero]/hero/friends/name

• Select all nodes named 'name' within a range of index 0 and index 2 (inclusion), reside under friends node {0:2}//query[name=hero]/hero/friends/name

• Select node named 'name', reside under any node, which reside under hero node /query[name=hero]/hero/.../name

• Select $withFriends variable reside directly under the root node named hero //query[name=hero]/withFriends[type=var]

• Select include directive first node reside under friends, which reside under root query node named hero /query[name=hero]/hero/friends/include[type=direc]

• Select the 'if' argument node, reside under the @include directive //.../include[type=direc]/if[type=arg]

• Select episode variable //.../episode[type=var]

How to use gqleXPath in the code:

SelectorFacade selectorFacade = new SelectorFacade();

String queryString = Files.readString(file.toPath());

// query {  Instrument(id: "1234") }
GqlNodeContext select = selectorFacade.select(queryString, "//query/Instrument /   Reference  /");

Use of SyntaxPath

String queryString = Files.readString(file.toPath());

SyntaxBuilder gqlexBuilder = new SyntaxBuilder();

gqlexBuilder.appendQuery();
gqlexBuilder.appendField("Instrument");
gqlexBuilder.appendField("Reference");

// query {  Instrument(id: "1234") }
GqlNodeContext select = selectorFacade.select(queryString, gqlexBuilder.build());

And finally we will dwell on an example that will illustrate the use of gqleXPath node selection GraphQL manipulation (AKA transform).

Here a mutation GraphQL document

mutation CreateReviewForEpisode($ep: Episode!, $review: ReviewInput!) {
  createReview(episode: $ep, review: $review) {
    stars
    commentary
    stars
    commentary
  }
}

The following java code will select and transform mutation document,

String queryString = Files.readString(sourceFile.toPath());
        
TransformBuilder transformBuilder = new TransformBuilder();
transformBuilder.addChildrenNode("//mutation[name=CreateReviewForEpisode]/createReview/stars",new Field("child_of_stars"))
        .addSiblingNode("//mutation[name=CreateReviewForEpisode]/createReview/stars",new Field("sibling_of_stars"))
        .updateNodeName("//mutation[name=CreateReviewForEpisode]/createReview/stars","star_new_name")
        .removeNode("//mutation[name=CreateReviewForEpisode]/createReview/commentary")
        .duplicateNode("//mutation[name=CreateReviewForEpisode]/createReview/sibling_of_stars", 10);

TransformExecutor transformExecutor = new TransformExecutor(transformBuilder);

RawPayload rawPayload = new RawPayload();
rawPayload.setQueryValue(queryString);

RawPayload executeRawPayload = transformExecutor.execute(rawPayload);

Description:

add new children node named: child_of_stars under gqleXPath: //mutation[name=CreateReviewForEpisode]/createReview/stars

Add new sibling node named: sibling_of_stars under gqleXPath selected node: //mutation[name=CreateReviewForEpisode]/createReview/stars

Set new node name: star_new_name value to the selected node by gqleXPath:

//mutation[name=CreateReviewForEpisode]/createReview/stars

Remove selected node by gqleXPath //mutation[name=CreateReviewForEpisode]/createReview/commentary

Duplicate selected gqleXPath node 10 times //mutation[name=CreateReviewForEpisode]/createReview/sibling_of_stars

Use TransformBuilder to build the transform plan, with selected node use of gqleXPath and the command to execute. The transform plan is load to the TransformExecutor, with the GraphQL payload.

The execution will result in a new GraphQL document,

mutation CreateReviewForEpisode($ep: Episode!, $review: ReviewInput!) {
  createReview(episode: $ep, review: $review) {
    sibling_of_stars
    star_new_name {
      child_of_stars
    }
    star_new_name {
      child_of_stars
    }
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
    sibling_of_stars
  }
}

Last example, will demonstrate the manipulation of directive from include to exclude

Here the query GraphQL document,

query Hero($episode: Episode, $withFriends: Boolean!) {
  hero(episode: $episode) {
    name
    friends **@include**(if: $withFriends) {
      name
    }
  }
}

Here the code:

        String queryString = Files.readString(file.toPath());

        // query {  Instrument(id: "1234") }
        GqlNodeContext includeDirectiveNode = selectorFacade.selectSingle(queryString, "//query[name=hero]/hero/friends/include[type=direc]");

        assertNotNull(includeDirectiveNode);

        assertTrue(includeDirectiveNode.getType().equals(DocumentElementType.DIRECTIVE));
        System.out.println("\nBefore manipulation:\n\n" + queryString);

        // Node newNode = new Field("new_name");
        Node excludeDirectiveNode = TransformUtils.updateNodeName(includeDirectiveNode, "exclude");

        String newGqlValue = gqlexWriter.writeToString(excludeDirectiveNode);

        System.out.println("\nAfter manipulation:\n\n" + newGqlValue);

        GqlNodeContext excludeUpdateNode = selectorFacade.selectSingle(newGqlValue, "//query[name=hero]/hero/friends/exclude[type=direc]");

        assertTrue(excludeUpdateNode.getType().equals(DocumentElementType.DIRECTIVE));

query Hero($episode: Episode, $withFriends: Boolean!) {
  hero(episode: $episode) {
    name
    friends @exclude(if: $withFriends) {
      name
    }
  }
}

The gqlex can be used during base code while the developer required to enrich GraphQL document with more fields, while querying server for data, or during manipulation of data in server, so the code can articulate the relevant fields to manipulate in the service side. The gqlex can also be utilize during integration or E2E testing, generating of synthetic GraphQL data, result with high velocity and managed solution.

I elaborate the following use cases with more details:

Synthetic GraphQL document creation Testing, mostly integration testing part will demands the ability to query GraphQL server with different queries and mutations.

Of course, the developer can maintain large list of example files to send to the server or to find and replace the relevant string in GraphQL document, but it is a cumbersome solution, hard to maintain etc.

The ability to manipulate the query or the mutation with ease way, use configuration that enlist the plan [gqleXPath, Transform Commands and Argument to execute] and execute the planץ

Configuration
  Plan
    steps
      step 1
         gqleXPath (String)
         transform_commands
           transform_command
               command
               argument_object_definition
      step n
         gqleXPath (String)
         transform_commands
           transform_command
               command
               argument_object_definition
  origin_file_to_manipulate

Configuration config = read_configuration_plan(plan_file);

config_verification()

build_plan -> ... use of TransformBuilder

new_graphql_document = execute_plan -> ... use of TransformExecuter

Versatility and an extremely high ability to produce synthetic GraphQL data and a high ability to verify the integrity of a GraphQL service.

Articulate GraphQL document on-the-fly Sometime you required to build query or mutation upon configuration on the fly or upon business logic, and send it to the GraphQL server, The gqlex library will assist you while doing it, The gqlex library does not support creation (only manipulation) of the skeleton file and will not support (as for now). The developer can create the skeleton GraphQL file, store the file in resource folder. skeleton file, means file with structure but without field only. And with relevant plan use of syntaxPath we can assemble the gqleXPath and set the plan strategy on the fly, use of TransformBuilder. And then use of TransformExecutor to run the plan.