如何在Spring-MongoDb聚合框架中使用$ cond *** 作

如何在Spring-MongoDb聚合框架中使用$ cond *** 作

如果使用

$cond

通过

$project

管道支持 *** 作员的当前Spring Data版本，则可以将其转换为（未测试）：

import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;import static org.springframework.data.mongodb.core.aggregation.ConditionalOperators.Cond.*;import org.springframework.data.mongodb.core.query.Criteria;Cond condOperation = ConditionalOperators.when(Criteria.where("start").is("EARLY"))   .thenValueOf("deltastart.start")   .otherwise("deltastart.end");Aggregation agg = newAggregation(project().and(condOperation).as("start"));AggregationResults<MyClass> results = mongoTemplate.aggregate(agg, MyClass.class); List<MyClass> myList = results.getMappedResults();

对于

$cond

在聚合 *** 作中不支持运算符的Spring-Data MongoDB版本，有一种解决方法是实现AggregationOperation接口以接收DBObject：

public class CustomProjectAggregationOperation implements AggregationOperation {    private DBObject operation;    public CustomProjectAggregationOperation (DBObject operation) {        this.operation = operation;    }    @Override    public DBObject toDBObject(AggregationOperationContext context) {        return context.getMappedObject(operation);    }}

然后

$project

，在聚合管道中将 *** 作实现为DBObject，该 *** 作与你拥有的 *** 作相同：

DBObject operation = (DBObject) new BasicDBObject(    "$project", new BasicDBObject(         "start", new BasicDBObject(     "$cond", new Object[]{  new BasicDBObject(      "$eq", new Object[]{ "$start", "EARLY"}  ),  "$deltastart.start",  "$deltastart.end"      })     ));

然后可以在TypeAggregation中使用它：

TypedAggregation<CustomClass> aggregation = newAggregation(CustomClass.class,    new CustomProjectAggregationOperation(operation));AggregationResults<CustomClass> result = mongoTemplate.aggregate(aggregation, CustomClass.class);