I have this mongodb query
db.getCollection('myCollection').aggregate(
[{
$project: {
length: {
$strLenCP: "$prefix"
}
}
}, {
$sort: {
length: -1
}
}]
)
that I want to use into a spring java project but I can't manage to write the correct java code (the sort is not the issue).
I tried this
Aggregation agg = newAggregation(project().andExpression("strLenCP(prefix)").as("prefixLength"));
AggregationResults < RequestSettingsWithPrefixLength > results = mongoTemplate.aggregate(agg, RequestSettings.class, RequestSettingsWithPrefixLength.class);
List < RequestSettingsWithPrefixLength > requestSettingsList = results.getMappedResults();
but I am getting a null key in agg JSON (debug mode):
{
"aggregate": "__collection__",
"pipeline": [{
{
"$project": {
"prefixLength": {
"null": ["$prefix"]
}
}
}]
}
}
I can see that my agg object has this projection operation:
expression -> strLenCP(prefix)
field -> AggregationField: AggregationField - name: prefixLength, target: prefixLength, synthetic: true
params -> []
I am not sure this is correct but I can't find any documentation that uses strLenCP. I only found this test that uses the strLenCP projection: https://github.com/spring-projects/spring-data-mongodb/blob/dc57b66adfd60b4d69d1d349b4fcfa4ab0da95e7/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/SpelExpressionTransformerUnitTests.java#L922
Could someone help please?
Cheers
The support for Mongo3.4 aggregation operators were added in 1.10.0.RC1. If you are okay with updating to release candidate version everything should just work fine.
Or you can try the following but you'll need to use 1.8.5 version.
Aggregation aggregation = newAggregation(
project().and(new AggregationExpression() {
@Override
public DBObject toDbObject(AggregationOperationContext aggregationOperationContext) {
return new BasicDBObject("$strLenCP", "$prefix");
}
}).as("prefixLength")
);
You can use expression project(...).and(valueOf("fieldName").lengthCP()).as("fieldLength")
@kairius answer isn't clear. This is how it should be done: Use StringOperators#valueOf followed by lengthCP():
TypedAggregation.project()
.and(StringOperators.valueOf("prefix").lengthCP())
.as("length")