Spring Data MongoDB without _class field on demand per class

NoTypeAlias.java

package io.noticeable.data.autoconfigure;

import java.lang.annotation.*;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface NoTypeAlias {
}

NoTypeAliasConfiguration.java

package io.noticeable.data.autoconfigure;

import jakarta.annotation.PostConstruct;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
import org.springframework.data.mongodb.core.mapping.MongoMappingContext;


@Configuration
public class NoTypeAliasConfiguration {

    private final ApplicationContext applicationContext;

    @Autowired
    public NoTypeAliasConfiguration(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @PostConstruct
    public void init() {
        final MappingMongoConverter converter = applicationContext.getBean(MappingMongoConverter.class);
        final MongoMappingContext mappingContext = applicationContext.getBean(MongoMappingContext.class);
        converter.setTypeMapper(new NoTypeAliasMongoTypeMapper(mappingContext));
    }

}

NoTypeAliasMongoTypeMapper.java

package io.noticeable.data.autoconfigure;

import org.bson.conversions.Bson;
import org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper;
import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
import org.springframework.data.util.TypeInformation;


public class NoTypeAliasMongoTypeMapper extends DefaultMongoTypeMapper {

    public NoTypeAliasMongoTypeMapper(MongoMappingContext mappingContext) {
        // Pass the mappingContext so alias resolution keep working
        super(DefaultMongoTypeMapper.DEFAULT_TYPE_KEY, mappingContext);
    }

    @Override
    public void writeType(final TypeInformation<?> info, final Bson sink) {
        // If the type is annotated with @NoTypeAlias, skip the _class field
        if (info.getType().isAnnotationPresent(NoTypeAlias.class)) {
            return;
        }
        // Otherwise, let the parent handle alias resolution
        super.writeType(info, sink);
    }

}

Then, you can use the annotation on your entity class as this:

@Document(collection = "publications")
@NoTypeAlias
public class Publication {
  // ...
}