Graphql工具:将实体类型映射到graphql类型 [英] Graphql Tools: Map entity type to graphql type

问题描述

我在spring应用程序中使用graphql java工具.我有一个这样的实体:

I'm using graphql java tools in my spring application. I have an entity like this:

@Entity
data class Image(
        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        @Column(nullable = false)
        val id: Long = 0
) {
    @Lob
    @Column(nullable = false)
    var image: Blob? = null
}

在GraphQL模式中，我想使用其他类型:

And in the GraphQL schema I want to have a different type:

type Image {
    id: ID!
    image: String!
}   

当然，由于架构解析异常，启动此操作将无效. 因此，我认为必须有可能在架构解析之间放置一些内容，以实现从Blob到String的映射.

Starting this won't work, of course, because of a schema parsing exception. So I thought it must be possible to put something in between the schema parsing to implement a mapping from Blob to String.

这在某种程度上可能吗?

Is this somehow possible here?

@Bean
fun schemaParserDictionary(): SchemaParserDictionary {
    return SchemaParserDictionary()
}

编辑

对不起，它不会提供架构解析异常.它将简单地将字节放入字符串中.但是我不能使用该字符串来创建图像.

Sorry, it won't give a schema parsing exception. It will simply put the bytes into a string. But I can't use that string then to create the image.

澄清

对不起，我想我对我的问题还不够清楚.我不需要知道如何将Blob转换为字符串.有很简单的解决方案.例如，我可以使用一个简单的API函数将字节码转换为base64:

Sorry, I guess I was not clear enough with my question. I don't need to know how to transform a blob into a string. There are very easy solutions for that. For example I can use a simple API function to transform byte code into base64:

val base64 = Base64.getEncoder().encodeToString(byteCode)

我想问的是如何告诉" graphql模式解析器以对特定字段使用该自定义"转换.因此，当我的实体对象具有数据类型为blob的字段image时，graphql会自动将其转换为string.但是字符串不包含我需要的内容.因此，我想针对该特定字段使用自定义的解析/映射/转换/任何方法.当然，通过引入另一个我不存储在数据库中的字段，我也可以轻松解决此问题:

What I tried to ask was how I can "tell" graphql schema parser to use that "custom" transformation for a specific field. So when my entity object has the field image with datatype blob graphql is automatically transforming this to a string. But the string does not contain the content that I need. So I want to use a custom parsing / mapping / transformation / whatever for that particularly field. Of course, I could also easily get around this by introducing another field which I do not store in the database:

@Entity
data class Image(
        @Id
        @GeneratedValue(strategy = GenerationType.SEQUENCE)
        @Column(nullable = false)
        val id: Long = 0
) {
    @Lob
    @Column(nullable = false)
    var image: Blob? = null

    @Transient
    var base64: String = ""
}

但是我可以通过graphql api进行查询:

but which I make queryable through the graphql api:

type Image {
    id: ID!
    image: String!
    base64: String!
}

type Images {
    images: [Image!]!
    totalCount: Int!
}

type Query {
    getImages: Images!
}

并将其设置在我的控制器中

And set it in my controller:

private fun getImages(): Images {
    var images: List<Image> = repository.findTop1000()

    images.forEach {
        it.base64 = Base64.getEncoder().encodeToString(it.image)

        queue.offer(it)
    }
}

但是如果我可以告诉graphql模式解析器这样做，那会更干净.

But it would be cleaner if I could tell the graphql schema parser to do that.

推荐答案

Kushal的答案提供了将Blob转换为String的代码片段.要进行这种转换，最好使用DTO.

Kushal's answer provides the snippets to convert a Blob to a String. To use this conversion, it is good practice to use DTO.

为此，请将您的graphql模式转换为:

To do so, transform your graphql schema to:

type ImageDTO {
    id: ID!
    image: String!
} 

并创建一个DTO类ImageDTO:

And create a DTO class ImageDTO:

public class ImageDTO {
    private Image entity;

    //Constructor
    public ImageDTO(Image image) {
         this.entity=image;
    }

    //Getters
    public Long getId() {
        return entity.getId();
    }

    public String getImage() {
        //convert the entity image and return it as String
        return Base64.getEncoder().encodeToString(entity.getImage());
    }
}

将DTO与实体分开可以更好地控制所传输的数据.

Separating the DTO from the entity grants you a finer control on the data transferred.

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