ReactiveMongo：如何使用投影

Question

我试图筛选出查询从MongoDB的文档与ReactiveMongo当password领域：

val projection = Json.obj("password" -> 0) 

def find(selector: JsValue, projection: Option[JsValue]) = { 
    val query = collection.genericQueryBuilder.query(selector) 
    projection.map(query.projection(_)) 
    query.cursor[JsValue].collect[Vector](perPage).transform(
    success => success, 
    failure => failure match { 
     case e: LastError => DaoException(e.message, Some(DATABASE_ERROR)) 
    } 
) 
} 

上面的代码没有任何影响。我也得到了password场。如果我尝试从蒙戈客户端的操作，那么它的工作原理和password没有返回：

db.users.find({ username: 'j3d' }, { password:0}) 

我缺少的东西？

Answer 1

这里是解决方案：

def find(selector: JsValue, projection: Option[JsValue]) = { 
    var query = collection.genericQueryBuilder.query(selector) 
    projection.map(query = query.projection(_)) 

    query.cursor[JsValue].collect[Vector](perPage).transform(
    success => success, 
    failure => failure match { 
     case e: LastError => DaoException(e.message, Some(DATABASE_ERROR)) 
    } 
) 
} 

或者：

def find(selector: JsValue, projection: Option[JsValue]) = { 
    val query = collection.genericQueryBuilder 
    .query(selector) 
    .projection(projection.getOrElse(Json.obj()) 

    query.cursor[JsValue].collect[Vector](perPage).transform(
    success => success, 
    failure => failure match { 
     case e: LastError => DaoException(e.message, Some(DATABASE_ERROR)) 
    } 
) 
} 

我希望帮助。