使用 MongoTemplate 时如何将类型从 ObjectId 转换为 Long？

Question

Normally when using spring data repositories, an object in which the result data can be stored is needed like the customer in this example: https://spring.io/guides/gs/accessing-data-mongodb/ .

In my case I'm trying to use an object which is declared in another project I'm importing using maven - let's call it MyDoc . The object has an attribute Long id while the document in the MongoDB has an addition field _id from type ObjectId . This btw is like this because the MongoDB serves as an archive and the actual id from MyDoc would not be unique.

In a service class I then use this the MongoTemplate to make database queries like this:

List<MyDoc> list = template.findAll(MyDoc.class, "DOCS");

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.bson.types.ObjectId] to type [java.lang.Long] 

How can I convert the ObjectId to a type of Long?

Alternately, I could, of course, use the java MongoDB driver but I wanted to reduce the number of dependencies to maintain since the MongoDB driver comes with the boot-starter-data-MongoDB dependency, and also hoped for a more intuitive way, in the end, to interact with the database like with the spring data repositories.

Answer 1

First thing is Long Id from MyDoc is not unique, so it cannot act as _id of mongoDB. Then you need to have one more _id field in your class. By Default Spring data mongoDB will map field named id to _id in dataBase. Essentially what you can do is create a wrapper class around MyDoc by extending it and then add new field of Type ObjectId and annotate it with @Id . By that way you will have unique index and also mongoTemplate will not try to convert _id of database to Long id