SpringBoot: Couchbase and the _class attribute

While learning new technology, we often face some barriers. Though this solvable or non-solvable barrier always ends up in making you learn some new things about the technology. A few days back while using Couchbase as my back-end DB in a Spring-boot Application , I encountered one problem.
So, this blog will brief you with the problem and solution.

Problem:

I have created a reactive Spring-boot application using reactive couchbase API. I have a use case of searching employee by its name. So, I have created a derivable query method.

Mono<Employee> findByEmpName(String name);

But sometimes, it was returning employee details or sometimes an empty response. Though the document was available in the bucket.

Observation:

Basically, we come up with the observation that whenever we try to add any document in our bucket, a field _class always get added as a part of JSON in a document. So, my bucket is having two types of document one with _class attribute and another without the _class attribute.
And based on the method findByEmpName mentioned above, the auto-generated query would look like :

WHERE (empName= name and _class = "edu.knoldus.employee.model.Employee")

It’s just like if your document consists _class, then it will deserialize the document, otherwise, you will get an empty response.

So, what we can do is, we can overwrite this auto-generated query. Now the question is how? 🤔

Solution:

We can use the @Query annotation and overwrite our auto-generated query. Let’s see how.

  @Query("#{#n1ql.selectEntity} where empName = $1")
    Mono<Employee> findByEmpName(String name);

Here,  #{#n1ql.selectEntity} is syntactic sugar for select * from bucket which fetches all the employee details by empName from couchbase.
And make sure not to add #{#n1ql.filter} in your query as it filters the document by _class field.
Hope you understand the above use case. Please feel free to comment below if you have any doubt or suggestions.

References:

Couchbase with Spring-Boot and Spring Data

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