java - 如果架构与数据库结构不同，如何将 graphql 与 jpa 一起使用

Question

有给定的数据库结构和 graphql 模式。幸运的是，它们有很多共同点，但不幸的是也存在一些差异。假设java中存在与以下数据库结构相匹配的实体。

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 架构被认为是这样的:

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

type Cow {
id: int!
milkInL: int!
nrOfLegs: int
}

该项目使用 11.0 版本的 graphql-java(估计我们应该很快更新)

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

graphql 工作正常，实现如下:

@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getGraphQlCowFromCowEntity和getGraphQlSheepFromSheepEntity。它使代码加倍，并且与 graphql 所假设的数据抽象直接冲突。通过这种设计，每次所有字段都通过 jpa 加载，而不仅仅是请求的字段。想象一下这是一个更加复杂的环境，具有更多的字段。

无法更改 graphql 架构，因为这不是我的责任，更改整个后端以匹配架构也不是我想要存档的内容。

亲切的问候

Answer 1

您应该使用 DTO。检索和发送实体对象是不好的做法，因为您不希望每次重构数据库模型时或在您的情况下更改 grahql api。您的 Sheep 和 Cow 对象是 DTO，但您需要某种方法将实体转换为 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)。

为了解决您对仅加载请求的数据的担忧，您希望 DTO 对象仅填充请求的字段。实现此目的的一种方法是，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，而不是填充所有字段。

public class Sheep {

    private SheepE entity;
    public Sheep(SheepE entity){
        this.entity=entity;
    }

    public getId() {
        return entity.getId();
    }

    public getLastTimeSheared() {
        return entity.getLastTimeSheared();
    }
    ...
}

请参阅我写给类似问题的答案:Graphql Tools: Map entity type to graphql type