问题
I'm currently writing an aggregation query for MongoDB in my Spring project in which I'm using $project operator. Within this operator I would like to compare two fields in order to return the result as projected "matches" key value. Here's the mongoDB shell equivalent (which works):
{$project:
{matches:
{$eq: ["$lastDate", "$meta.date"]}
}
}
I've read Spring Data MongoDB documentation and found some useful info about ProjectionOperator's 'andExpression' method which uses SpEL. The result Java code of my investigation was:
new ProjectionOperation().andExpression("lastDate == meta.date").as("matches")
Unfortunately I'm receiving exception:
java.lang.IllegalArgumentException: Unsupported Element:
org.springframework.data.mongodb.core.spel.OperatorNode@70c1152a Type: class org.springframework.data.mongodb.core.spel.OperatorNode You probably have a syntax error in your SpEL expression!
As far as I've checked, Spring Data MongoDB handles all Arithmetic operators correctly but cannot handle the comparison ones. Therefore I want to ask is there any other way to create such query with Spring Data MongoDB? Or maybe I don't know something crucial about SpEL?
回答1:
I resolved this issue by passing JSON aggregate command (created with DBObjects in order to preserve flexibility of the query) to MongoDB, i.e.:
MongoOperations#executeCommand(DBObject command)
来源：https://stackoverflow.com/questions/27080374/spring-data-mongodb-eq-within-project-support