How can I implement addFields mongoDB query in Java

问题

I have found several example at StackOverFlow related to addFields in Aggregation. But no one implemented in Java.

db.getCollection('myDocument').aggregate([
    {$match : {"metaId.ref.uuid" : "d6112808-1ce1-4545-bd52-cf55bc4ed25e"}},
    {$lookup: {from: "simple", localField: "someId.ref.uuid", foreignField: "uuid", 
    as: "simple"}},
    {"$unwind": "$simple"},
    {"$addFields": { "metaId.ref.name" : "$simple.name" }}
])

I am not able to Implement In Java Correctly:-- Not getting proper procedure

   LookupOperation lookupOperation =LookupOperation.newLookup().from("simple").localField("execId.ref.uuid").foreignField("uuid").as("simple");
            Aggregation myDocAggr = newAggregation(match(Criteria.where("metaId.ref.uuid").is(someUUID)), group("uuid").max("version").as("version"),
                    lookupOperation,
                    Aggregates.unwind(""),
                Aggregates.addFields(fields));
            Document document =new Document();
            AggregationResults<String> myDocAggrResults = mongoTemplate.aggregate(myDocAggr , myDocument, myDocument.class);
            List<String> mydocumentList = myDocAggrResults .getMappedResults();

Not able to use unwind and addFields, this is sample java code, but it is not ok. Please help me. Thanks in advance

回答1:

You are mixing the java driver Aggregates method with Spring Aggregation methods.

Also $addFields is still not supported in spring mongo.

You have to use below aggregation.

import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
Aggregation myDocAggr = newAggregation(
       match(Criteria.where("metaId.ref.uuid").is(someUUID)), 
       group("uuid").max("version").as("version"),
       lookup("simple","execId.ref.uuid","uuid","simple"),
       unwind("simple"),
       new AggregationOperation(){ 
         @Override 
         public Document toDocument(AggregationOperationContext aoc) {
            return new Document("$addFields",new Document("metaId.ref.name","$simple.name"));
         }
      }
)
List<Document> mydocumentList=mongoTemplate.aggregate(myDocAggr,"myDocument",Document.class).getMappedResults();

回答2:

Although the $addFields are not supported by spring mongo you can implement it by yourself:

import org.bson.Document;
import org.springframework.data.mongodb.core.aggregation.*;
import java.util.LinkedHashMap;
import java.util.Map;

public class AddFieldsOperation implements FieldsExposingAggregationOperation {
    private Map<String, Object> fields = new LinkedHashMap<>();

    public AddFieldsOperation(String field, AggregationExpression expression) {
        addField(field, expression);
    }

    public AddFieldsOperation addField(String field, AggregationExpression expression) {
        this.fields.put(field, expression.toDocument(Aggregation.DEFAULT_CONTEXT));
        return this;
    }

    @Override
    public Document toDocument(AggregationOperationContext context) {
        Document doc = new Document();
        fields.forEach(doc::append);
        return new Document("$addFields", doc);
    }

    @Override
    public boolean inheritsFields() {
        return true;
    }

    @Override
    public ExposedFields getFields() {
        final String[] fieldsArray = fields.keySet().toArray(new String[0]);
        return ExposedFields.synthetic(Fields.fields(fieldsArray));
    }

And use it like this:

...
ArithmeticOperators.Add value1 = ArithmeticOperators.Add.valueOf(0);
ArithmeticOperators.Add value2 = ArithmeticOperators.Add.valueOf(0);
AddFieldsOperation addFields
            = new AddFieldsOperation("value1", value1)
            .addField("value2", value2);
pipeline.add(addFields);
...
Add value1PlusValue2 = Add.valueOf("$value1").add("$value2");
...

Hope it will help someone.

来源：https://stackoverflow.com/questions/53261607/how-can-i-implement-addfields-mongodb-query-in-java