fix(GH-220): Cannot nest multiple queries on the same table (#222)

* fix: plural attributes double wrapping in list type

* fix: Applied consistent behaviors for JOIN and EXISTS criteria expressions

* fix: add tests

* feat: Added isShouldClearContext configuration to invoke clear() for EM

* fixme: Added failing tests to fix some time later

* chore: find and replace '\n' with ''

* fix: remove wrong hint

* fix: Added test for  many-2- many query using both sides of the relationship

* Revert "feat: Added isShouldClearContext configuration to invoke clear() for EM"

This reverts commit c5ac022.

* fix: Corrected StarwarsQueryExecutor failing unit tests

Author: igdianov

graphql-jpa-query-example-model-starwars/src/main/java/com/introproventures/graphql/jpa/query/schema/model/starwars/Character.java

@@ -30,6 +30,7 @@
 import javax.persistence.OrderBy;
 
 import com.introproventures.graphql.jpa.query.annotation.GraphQLDescription;
+
 import lombok.EqualsAndHashCode;
 import lombok.Getter;
 import lombok.Setter;
@@ -40,7 +41,7 @@
 @Getter
 @Setter
 @ToString
-@EqualsAndHashCode(exclude={"appearsIn","friends"}) // Fixes NPE in Hibernate when initializing loaded collections #1
+@EqualsAndHashCode(exclude={"appearsIn","friends", "friendsOf"}) // Fixes NPE in Hibernate when initializing loaded collections #1
 public abstract class Character {
 
     @Id
@@ -58,6 +59,10 @@ public abstract class Character {
     @OrderBy("name ASC")
     Set<Character> friends; 
 
+    @ManyToMany(fetch=FetchType.LAZY, mappedBy = "friends")
+    @OrderBy("name ASC")
+    Set<Character> friendsOf;     
+    
     @GraphQLDescription("What Star Wars episodes does this character appear in")
     @ElementCollection(targetClass = Episode.class, fetch=FetchType.LAZY)
     @Enumerated(EnumType.ORDINAL)

graphql-jpa-query-schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java

@@ -332,7 +332,7 @@ private GraphQLInputObjectType computeSubqueryInputType(ManagedType<?> managedTy
                                           .build()            
             )
             .fields(managedType.getAttributes().stream()
-                                               .filter(this::isValidAssociation)    
+                                               .filter(Attribute::isAssociation)
                                                .filter(this::isNotIgnored)
                                                .filter(this::isNotIgnoredFilter)
                                                .map(this::getWhereInputRelationField)
@@ -404,7 +404,7 @@ private GraphQLInputObjectType computeWhereInputType(ManagedType<?> managedType)
                                                .collect(Collectors.toList())
             )
             .fields(managedType.getAttributes().stream()
-                                               .filter(this::isValidAssociation)    
+                                               .filter(Attribute::isAssociation)
                                                .filter(this::isNotIgnored)
                                                .filter(this::isNotIgnoredFilter)
                                                .map(this::getWhereInputRelationField)
@@ -853,7 +853,9 @@ else if (isElementCollection(attribute)) {
             Type foreignType = ((PluralAttribute) attribute).getElementType();
 
             if(foreignType.getPersistenceType() == Type.PersistenceType.BASIC) {
-            	return new GraphQLList(getGraphQLTypeFromJavaType(foreignType.getJavaType()));
+                GraphQLType graphQLType = getGraphQLTypeFromJavaType(foreignType.getJavaType());
+                
+            	return input ? graphQLType : new GraphQLList(graphQLType);
             }
         }
 
@@ -897,11 +899,6 @@ protected final boolean isValidInput(Attribute<?,?> attribute) {
                 attribute.getPersistentAttributeType() == Attribute.PersistentAttributeType.EMBEDDED;
     }
 
-    protected final boolean isValidAssociation(Attribute<?,?> attribute) {
-        return isOneToMany(attribute) || isToOne(attribute);
-    }
-
-
     private String getSchemaDescription(Attribute<?,?> attribute) {
         return EntityIntrospector.introspect(attribute.getDeclaringType())
                                  .getSchemaDescription(attribute.getName())

graphql-jpa-query-schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/JpaPredicateBuilder.java

@@ -30,14 +30,14 @@
 import java.util.Collection;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.UUID;
 
 import javax.persistence.criteria.CriteriaBuilder;
 import javax.persistence.criteria.Expression;
 import javax.persistence.criteria.From;
-import javax.persistence.criteria.Join;
 import javax.persistence.criteria.Path;
 import javax.persistence.criteria.Predicate;
 import javax.persistence.metamodel.EntityType;
@@ -730,27 +730,21 @@ else if(Collection.class.isAssignableFrom(type)) {
             // collection join for plural attributes
             if(PluralAttribute.class.isInstance(from.getModel()) 
                     || EntityType.class.isInstance(from.getModel())) {
+                Expression<? extends Collection<Object>> expression = from.get(filter.getField());
                 Predicate predicate;
-                
-                if(EntityType.class.isInstance(from.getModel())) {
-                    From<?,?> join = null;
 
-                    for(Join<?,?> fetch: from.getJoins()) {
-                        if(fetch.getAttribute().getName().equals(filter.getField()))
-                            join = (From<?,?>) fetch;
-                    }
+                if(Collection.class.isInstance(filter.getValue())) {
+                    List<Predicate> restrictions = new ArrayList<>();
 
-                    if(join == null) {
-                        join = (From<?,?>) from.join(filter.getField());
-                    }
+                    Collection.class.cast(filter.getValue())
+                                    .forEach(v -> restrictions.add(cb.isMember(v, expression)));
+                                       
+                    predicate = cb.and(restrictions.toArray(new Predicate[] {}));
 
-                    predicate = join.in(value);
                 } else {
-                    Expression<? extends Collection<Object>> expression = from.get(filter.getField()); 
-                    
                     predicate = cb.isMember(filter.getValue(), expression);
                 }
-
+                
                 if(filter.anyMatch(Criteria.NIN, Criteria.NE)) {
                    return cb.not(predicate);
                 }