如果模式与数据库结构不同，如何将graphql与jpa结合使用

Question

有一个给定的数据库结构和graphql模式。幸运的是，他们有很多共同点，但不幸的是有一些不同。假设java中存在与以下数据库结构匹配的实体。

SQL:

TABLE ANIMAL
+ID NUMBER(19)
+NR_OF_LEGS NUMBER(19)
TABLE SHEEP
+ID NUMBER
+LAST_TIME_SHEARED DATETIME
+ANIMAL_ID NUMBER(19)
TABLE COW
+MILK_IN_L NUMBER(3)
+ANIMAL_ID NUMER(19)

Java：

@Entity
@Table(name = "ANIMAL")
public class Animal
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(name="nrOfLegs", nullable=false)
private long nrOfLegs;
}

@Entity
@Table(name = "SHEEP")
public class SheepE
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(name="lastTimeSheared", nullable=false)
private Datetime lastTimeSheared;
@ManyToOne(targetEntity = AnimalE.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = true)
@JoinColumn(name = "animalId", nullable = false, insertable = false, updatable = false)   
private Animal animal;
}

@Entity
@Table(name = "COW")
public class CowE
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(name="milkInL", nullable=false)
private int milkInL;
@ManyToOne(targetEntity = AnimalE.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = true)
@JoinColumn(name = "animalId", nullable = false, insertable = false, updatable = false)   
private Animal animal;
}

现有的GraphQl模式被认为是这样的：

type Sheep{
id: int!
lastTimeSheard: String!
nrOfLegs: int!
}
type Cow {
id: int!
milkInL: int!
nrOfLegs: int
}

该项目在11.0版本中使用graphql-java(猜测我们应该很快更新(

<dependency>
<groupId>com.graphql-java</groupId>
<artifactId>graphql-java</artifactId>
<version>11.0</version>
</dependency>

graphql运行良好，实现方式如下：

@Component
public class GraphQLProvider {
@Autowired
GraphQLDataFetchers graphQLDataFetchers;
private GraphQL graphQL;
@PostConstruct
public void init() {this.graphQL = /*init;*/null;}
private RuntimeWiring buildWiring() {
RuntimeWiring.Builder b = RuntimeWiring.newRuntimeWiring()
.type(TypeRuntimeWiring.newTypeWiring("Query")
.dataFetcher("freightCarrier", graphQLDataFetchers.getCow()))
.type(TypeRuntimeWiring.newTypeWiring("Query")
.dataFetcher("personCarrier", graphQLDataFetchers.getSheep())));
return b.build();
}
}
@Component
public class GraphQLDataFetchers {
@AutoWired
private CowRepository cowRepo;
@AutoWired
private sheepRepository sheepRepo;
public DataFetcher getCow() {
DataFetcher dataFetcher = (DataFetchingEnvironment dfe) -> {
int id = dfe.getArgument("id");
return getGraphQlCowFromCowEntity(cowRepo.getById(id));//dirty!
};
return dataFetcher;
}
public DataFetcher getCow() {
DataFetcher dataFetcher = (DataFetchingEnvironment dfe) -> {
int id = dfe.getArgument("id");
return getGraphQlSheepFromSheepEntity(cowRepo.getById(id));//dirty!
};
return dataFetcher;
}
private Cow getGraphQlCowFromCowEntity(CowE ce){//dirty!
return new Cow(ce.getId(), ce.getMilkInL(),ce.getLegs());
}
private Sheep getGraphQlSheepFromSheepEntity(SheepE se){//dirty!
return new Sheep(se.getId(), se.getLastTime(),se.getLegs());
}

public class Sheep
private long id;
private Datetime lastTimeSheared;
private int nrOfLegs;
public Sheep(long id, DateTime lasttimeSheared, int nrOfLegs){
//u know what happens here
}
}
public class Cow
private long id;
private int milkInL;
private int nrOfLegs;
public Sheep(long id, int milkInL, int nrOfLegs){
//u know what happens here
}
}

那么如何摆脱getGraphQlCowEntity和

GetGraphQl SheepFromSheepEntitygraphql模式不能更改，因为这不是我的责任，更改整个后端以匹配模式也不是我想要存档的。

问候

Answer 1

您应该使用DTO。检索和发送实体对象是一种糟糕的做法，因为您不希望每次重构数据库模型时或者在您的情况下更改grahqlapi。您的Sheep和Cow对象是DTO，但您需要一些方法将实体转换为DTO(getGraphQlCowFromCowEntity很好，但您可以使用多态性CowEntity.toDTO()，或者让服务层进行转换，有很多方法可以做到这一点(。

为了解决只加载请求的数据的问题，您希望DTO对象只填充请求的字段。一种方法是，不填充所有字段，而是让DTO拥有对实体对象的引用，并仅在请求时从实体对象检索数据。

public class Sheep {
private SheepE entity;
public Sheep(SheepE entity){
this.entity=entity;
}
public getId() {
return entity.getId();
}
public getLastTimeSheared() {
return entity.getLastTimeSheared();
}
...
}

请看我写的一个类似问题的答案：Graphql工具：将实体类型映射到Graphql类型