Morphia展开聚合返回的结果与Mongo数据库查询不同？

Question

我试图在这里做一个简单的MongoDB聚合。 基本上我有这样的文件：

{
timestampInMs: 1444094140442,
records: [
{
value: "testvalue",
experiment: {
id: "56105b0af2763b25806d1365",
name: "integrationtest-kkkk",
created: "2015-10-03T22:47:38.479+0000",
updated: null
},
sensorId: "testsensor",
dataType: 1
},
{
value: "testvalue2",
experiment: {
id: "56105b0af2763b25806d1365",
name: "integrationtest-kkkk",
created: "2015-10-03T22:47:38.479+0000",
updated: null
},
sensorId: "testsensor2",
dataType: 1
},
{
value: "testvalue3",
experiment: {
id: "56105b0af2763b25806d1365",
name: "integrationtest-kkkk",
created: "2015-10-03T22:47:38.479+0000",
updated: null
},
sensorId: "testsensor3",
dataType: 1
},
{
value: "testvalue4",
experiment: {
id: "56105b0af2763b25806d1365",
name: "integrationtest-kkkk",
created: "2015-10-03T22:47:38.479+0000",
updated: null
},
sensorId: "testsensor4",
dataType: 1
}
],
created: "2015-10-06T01:15:40.501+0000",
updated: "2015-10-06T01:15:40.528+0000"
}

Java模型如下所示

@Entity("sensordatadocs")
@Indexes ({
    @Index(fields = @Field("timestampInMs"), options = @IndexOptions(name = "timestamp_ms_index"))
})
public class DbSensorDataDocument {

    @Id
    // Should be milliseconds since Epoch
    private Long timestampInMs;

    @Embedded
    private List<DbSensorDataRecord> records;

    private Date created;

    private Date updated;
}

public class DbSensorDataRecord {

    private String value;

    @Reference
    private Experiment experiment;

    private String sensorId;

    private int dataType;
}

当我使用数据库查询时

db.sensordatadocs.aggregate([{$unwind: "$records"}])

它给了我4个文档，每个文档的“记录”包含一个与原始数组中的项目相对应的项目。 但是，当我使用Morphia的API时，如下所示：

Iterator<DbSensorDataDocument> iter = datastore.createAggregation(DbSensorDataDocument.class)
        .unwind("records").aggregate(DbSensorDataDocument.class);

它将返回如下结果：

{
timestampInMs: 1444094140442,
sensorId: "testsensor",
value: "testvalue",
experimentId: "56105b0af2763b25806d1365",
dataType: 1
},
{
timestampInMs: 1444094140442,
sensorId: "testsensor",
value: "testvalue",
experimentId: "56105b0af2763b25806d1365",
dataType: 1
},
{
timestampInMs: 1444094140442,
sensorId: "testsensor",
value: "testvalue",
experimentId: "56105b0af2763b25806d1365",
dataType: 1
},
{
timestampInMs: 1444094140442,
sensorId: "testsensor",
value: "testvalue",
experimentId: "56105b0af2763b25806d1365",
dataType: 1
}

这是我的迭代代码的样子：

while (iter.hasNext()) {
            DbSensorDataDocument doc = iter.next();
            final SensorDataRecord record = SensorDataUtils.flattenSensorDataDocument(doc);  
            result.add(record);
        }

请注意，项目数是正确的，但是，“记录”中的值是错误的， 实际上，它们仅是 “原始数组中第一项”的值 。 为什么会这样呢？ 请帮忙。 谢谢！

Morphia版本1.0.1

Answer 1

该行为的原因是Morphia缓存问题。 在您的情况下，Morphia将DbSensorDataDocument实体的所有结果视为同一行（由于相同的主键timestampInMs ），并返回缓存的版本 。

要解决此问题，必须从具有聚合投影的结果中排除字段timestampInMs ：

Iterator<DbSensorDataDocument> iter = datastore.createAggregation(DbSensorDataDocument.class)
        .unwind("records").project(
 Projection.projection("timestampInMs").suppress(), 
 Projection.projection("XXXXXX").aggregate(DbSensorDataDocument.class);

其中XXXXX是您要包括的字段。