graphql-java 循环类型依赖
graphql-java cyclic types dependencies
我在尝试构建相互依赖的类型时遇到了障碍,这是代码:
import graphql.schema.GraphQLObjectType;
import static graphql.schema.GraphQLObjectType.newObject;
import static graphql.Scalars.*;
import graphql.schema.GraphQLFieldDefinition;
import graphql.schema.GraphQLList;
import static graphql.schema.GraphQLFieldDefinition.newFieldDefinition;
public class GraphQLTypes {
private GraphQLObjectType studentType;
private GraphQLObjectType classType;
public GraphQLTypes() {
createStudentType();
createClassType();
}
void createStudentType() {
studentType = newObject().name("Student")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("currentClass").type(classType).build())
.build();
}
void createClassType() {
classType = newObject().name("Class")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("students").type(new GraphQLList(studentType)).build())
.build();
}
}
不可能实例化这个 class,因为我得到这个异常
Caused by: graphql.AssertException: type can't be null
at graphql.Assert.assertNotNull(Assert.java:10)
at graphql.schema.GraphQLFieldDefinition.<init>(GraphQLFieldDefinition.java:23)
at graphql.schema.GraphQLFieldDefinition$Builder.build(GraphQLFieldDefinition.java:152)
at graphql_types.GraphQLTypes.createStudentType(GraphQLTypes.java:26)
at graphql_types.GraphQLTypes.<init>(GraphQLTypes.java:19)
显然 classType 在 createStudentType() 引用它时尚未实例化。我该如何解决这个问题?
您是否尝试使用 new GraphQLTypeReference("ForwardType")
?我说的是这个 https://github.com/graphql-java/graphql-java#recursive-type-references
GraphQLTypeReference 确实是答案。应该这样做:
import graphql.schema.GraphQLList;
import graphql.schema.GraphQLObjectType;
import graphql.schema.GraphQLTypeReference;
import static graphql.Scalars.GraphQLString;
import static graphql.schema.GraphQLFieldDefinition.newFieldDefinition;
import static graphql.schema.GraphQLObjectType.newObject;
public class GraphQLTypes {
private GraphQLObjectType studentType;
private GraphQLObjectType classType;
public GraphQLTypes() {
createStudentType();
createClassType();
}
void createStudentType() {
studentType = newObject().name("Student")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("currentClass").type(new GraphQLTypeReference("Class")).build())
.build();
}
void createClassType() {
classType = newObject().name("Class")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("students").type(new GraphQLList(studentType)).build())
.build();
}
}
我在尝试构建相互依赖的类型时遇到了障碍,这是代码:
import graphql.schema.GraphQLObjectType;
import static graphql.schema.GraphQLObjectType.newObject;
import static graphql.Scalars.*;
import graphql.schema.GraphQLFieldDefinition;
import graphql.schema.GraphQLList;
import static graphql.schema.GraphQLFieldDefinition.newFieldDefinition;
public class GraphQLTypes {
private GraphQLObjectType studentType;
private GraphQLObjectType classType;
public GraphQLTypes() {
createStudentType();
createClassType();
}
void createStudentType() {
studentType = newObject().name("Student")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("currentClass").type(classType).build())
.build();
}
void createClassType() {
classType = newObject().name("Class")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("students").type(new GraphQLList(studentType)).build())
.build();
}
}
不可能实例化这个 class,因为我得到这个异常
Caused by: graphql.AssertException: type can't be null
at graphql.Assert.assertNotNull(Assert.java:10)
at graphql.schema.GraphQLFieldDefinition.<init>(GraphQLFieldDefinition.java:23)
at graphql.schema.GraphQLFieldDefinition$Builder.build(GraphQLFieldDefinition.java:152)
at graphql_types.GraphQLTypes.createStudentType(GraphQLTypes.java:26)
at graphql_types.GraphQLTypes.<init>(GraphQLTypes.java:19)
显然 classType 在 createStudentType() 引用它时尚未实例化。我该如何解决这个问题?
您是否尝试使用 new GraphQLTypeReference("ForwardType")
?我说的是这个 https://github.com/graphql-java/graphql-java#recursive-type-references
GraphQLTypeReference 确实是答案。应该这样做:
import graphql.schema.GraphQLList;
import graphql.schema.GraphQLObjectType;
import graphql.schema.GraphQLTypeReference;
import static graphql.Scalars.GraphQLString;
import static graphql.schema.GraphQLFieldDefinition.newFieldDefinition;
import static graphql.schema.GraphQLObjectType.newObject;
public class GraphQLTypes {
private GraphQLObjectType studentType;
private GraphQLObjectType classType;
public GraphQLTypes() {
createStudentType();
createClassType();
}
void createStudentType() {
studentType = newObject().name("Student")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("currentClass").type(new GraphQLTypeReference("Class")).build())
.build();
}
void createClassType() {
classType = newObject().name("Class")
.field(newFieldDefinition().name("name").type(GraphQLString).build())
.field(newFieldDefinition().name("students").type(new GraphQLList(studentType)).build())
.build();
}
}