我有一个聚合管道,其中包括一个像这样的项目:
$project: { start: { $cond: { if: { $eq: ["$start", "EARLY"] }, then: "$deltastart.start", else: "$deltastart.end" } },... },...
在mongo shell中可以正常工作。如何在Spring-Mongodb中使用Aggregation框架表达这一点?我见过ProjectionOperationBuilder,ExpressionProjectionOperationBuilder类型,但没有一个示例如何使用它们……有什么建议吗?
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):
$cond
$project
import static org.springframework.data.mongodb.core.aggregation.Aggregation.*; import static org.springframework.data.mongodb.core.aggregation.ConditionalOperators.Cond.*; import org.springframework.data.mongodb.core.query.Criteria; Cond condOperation = ConditionalOperators.when(Criteria.where("start").is("EARLY")) .thenValueOf("deltastart.start") .otherwise("deltastart.end"); Aggregation agg = newAggregation(project().and(condOperation).as("start")); AggregationResults<MyClass> results = mongoTemplate.aggregate(agg, MyClass.class); List<MyClass> myList = results.getMappedResults();
对于$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);