如果使用
$cond通过
$project管道支持操作员的当前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在聚合操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
$project，在聚合管道中将操作实现为DBObject，该操作与你拥有的操作相同：
DBObject operation = (DBObject) new BasicDBObject( "$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);
