在mongo (3.6) shell中,我可以执行以下聚合操作来将“_id”投影并重命名为其他名称:
db.collection.aggregate([
{ $group : { _id : ... },
{ $project : { '_id': 0, // exclude the id field
'name' : '$_id', // project the "old" id value to the "name" field
...
}
}
])
我需要使用spring-data-mongo(通过Spring Boot 2.3.1)进行翻译。 我可以使用以下ProjectionOperation来排除id字段:
project().andExclude("_id")
然而,到目前为止我无法重命名id字段。 以下任何一种都不起作用:
my first guess
project().and("_id").as("name")
as suggested here
project().andExpression("_id").as("name")
这应该不难,但我找不出自己缺少什么。
编辑:数据样本和完整聚合管道以重现失败
使用以下文档:
{
"_id" : ObjectId("5a0c7a3135587511c9247db4"),
"_class" : "task",
"category" : "green",
"status" : "OK"
}
{
"_id" : ObjectId("5a0cd21d35587511c9247db8"),
"_class" : "task",
"category" : "red",
"status" : "KO"
}
领域对象:
@Document(collection = "tasks")
@TypeAlias("task")
public class Task {
@Id
private String id;
private String status;
private String category;
// getters/setters omitted
}
以下是聚合内容:
Aggregation a = Aggregation.newAggregation(
group("status", "category").count().as("count"),
group("_id.category").push(
new Document("k", "$_id.status").append("v", "$count"))
.as("counts"),
project().and(arrayToObject("$counts")).as("counts"),
// this final stage fails with: a java.lang.IllegalArgumentException: Invalid reference '_id'!
project().and("_id").as("name").andExclude("_id")
);
mongotemplate.aggregate(a, "tasks", org.bson.Document.class)
在最后一个管道阶段之前,聚合会给出:
[ { "_id" : "green", "counts" : { "OK" : 1 } },
{ "_id" : "red", "counts" : { "KO" : 1 } } ]
所以我们应该能够将“_id”投影到“name”,但实际上我们得到了这个:
java.lang.IllegalArgumentException: Invalid reference '_id'!
at org.springframework.data.mongodb.core.aggregation.ExposedFieldsAggregationOperationContext.getReference(ExposedFieldsAggregationOperationContext.java:114) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.ExposedFieldsAggregationOperationContext.getReference(ExposedFieldsAggregationOperationContext.java:77) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.ProjectionOperation$ProjectionOperationBuilder$FieldProjection.renderFieldValue(ProjectionOperation.java:1445) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.ProjectionOperation$ProjectionOperationBuilder$FieldProjection.toDocument(ProjectionOperation.java:1432) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.ProjectionOperation.toDocument(ProjectionOperation.java:261) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.AggregationOperation.toPipelineStages(AggregationOperation.java:55) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.AggregationOperationRenderer.toDocument(AggregationOperationRenderer.java:56) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.aggregation.Aggregation.toPipeline(Aggregation.java:721) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.AggregationUtil.createPipeline(AggregationUtil.java:95) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.MongoTemplate.doAggregate(MongoTemplate.java:2118) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.MongoTemplate.aggregate(MongoTemplate.java:2093) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
at org.springframework.data.mongodb.core.MongoTemplate.aggregate(MongoTemplate.java:1992) ~[spring-data-mongodb-3.0.1.RELEASE.jar:3.0.1.RELEASE]
我已经找到了一个解决方法(见下文),但仍然好奇为什么上面显示的聚合失败了。我不明白为什么"_id"引用没有正确地显示出来。
成功的解决方法:
Aggregation a = Aggregation.newAggregation(
group("status", "category").count().as("count"),
group("_id.category").push(
new Document("k", "$_id.status").append("v", "$count"))
.as("counts"),
project().and(arrayToObject("$counts")).as("counts"),
// the following works
addFields().addFieldWithValue("name", "$_id").build(),
project().andExclude("_id").andExclude("counts")
);
对于那些无法弄清如何将MongoDB聚合转换为Spring Data Mongo聚合的人,可以使用以下解决方法:https://dev59.com/6VIH5IYBdhLWcg3wa9po#59726492
and("_id").as("name")
部分没有提供预期的结果。 - Marc Tarinproject().andExclude("_id").and("_id").as("name")
时,出现了一些崩溃问题... 在好好睡一晚后,我会深入研究它 ;) - Marc TarinarrayToObject
部分,但如果我们跳过/忽略它,这个单行解决方案同样有效:project("count").andExclude("_id").and("_id").as("name")
或者如果你想让它更易读一些:project().and("_id").as("name").andExclude("_id").andInclude("count")
- ktamas