feat: add equals criteria support for custom attributes types

[igdianov]

This PR adds support for EQ predicate with custom attribute types annotated with @Convert, i.e.

Given entity class with custom attribute:

@Entity("TaskVariable")
public TaskVariableEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String type;

    private String name;

    @Convert(converter = VariableValueJsonConverter.class)
    @Column(columnDefinition="text")
    private VariableValue<?> value;
}

And custom attribute value implementation with provided constructor having single Object argument :

public class VariableValue<T> {

    private T value;

    public VariableValue() {
    }
    // Required constructor
    public VariableValue(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }
}    

And AttributeConverter class:

public class VariableValueJsonConverter implements AttributeConverter<VariableValue<?>, String> {

    private static ObjectMapper objectMapper = new ObjectMapper()
            .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

    public VariableValueJsonConverter() {
    }

    @Override
    public String convertToDatabaseColumn(VariableValue<?> variableValue) {
        try {
            return objectMapper.writeValueAsString(variableValue);
        } catch (JsonProcessingException e) {
            throw new QueryException("Unable to serialize variable.", e);
        }
    }

    @Override
    public VariableValue<?> convertToEntityAttribute(String dbData) {
        try {
            return objectMapper.readValue(dbData, VariableValue.class);
        } catch (IOException e) {
            throw new QueryException("Unable to deserialize variable.", e);
        }
    }
    
}

With the following values stored as Json:

insert into TASK_VARIABLE (name, type, value) values
  ('variable1', 'string', '{"value":"data"}'),
  ('variable2', 'boolean', '{"value":true}'),
  ('variable3', 'object', '{"value":null}'),
  ('variable4', 'json', '{"value":{"key":"data"}}'),
  ('variable5', 'double', '{"value":1.2345}'),
  ('variable6', 'int', '{"value":12345}'),
  ('variable7', 'json', '{"value":[1,2,3,4,5]}');	

When the following query with EQ predicate for value attribute is excuted:

query {
  TaskVariables(where: {
    name: {EQ: "variable2"}
    value: {EQ: true}
  }) {
    select {
       name
       value
    }
  }
}

Then the result is as follows:

{
  "data": {
    "TaskVariables": {
      "select": [
        {
          "name": "variable2",
          "value": true
        }
      ]
    }
  }
}

See tests for other examples: https://github.com/introproventures/graphql-jpa-query/pull/133/files#diff-6d177f64d7dab4deb5f58343b51bd18aR332

[codecov]

Codecov Report

Merging #133 into master will increase coverage by 0.31%.
The diff coverage is 61.53%.

@@             Coverage Diff              @@
##             master     #133      +/-   ##
============================================
+ Coverage     68.08%   68.39%   +0.31%     
- Complexity      400      405       +5     
============================================
  Files            33       33              
  Lines          2068     2079      +11     
  Branches        307      311       +4     
============================================
+ Hits           1408     1422      +14     
+ Misses          535      531       -4     
- Partials        125      126       +1

Impacted Files	Coverage Δ	Complexity Δ
...hql/jpa/query/schema/impl/JpaPredicateBuilder.java	47.48% <61.53%> (+0.85%)	44 <0> (+2)	⬆️
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	74.8% <0%> (+1.04%)	130% <0%> (+2%)	⬆️
...ventures/graphql/jpa/query/schema/JavaScalars.java	46.66% <0%> (+1.25%)	5% <0%> (+1%)	⬆️

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