如何在 Spring Data MongoDB 中使用 $arrayElemAt 运算符 [英] How to use $arrayElemAt operator in Spring Data MongoDB

问题描述

$arrayElemAt MongoDB 3.2 版中的新内容.

$arrayElemAt new in MongoDB version 3.2.

db.users.aggregate([
{
 $project:
  {
     name: 1,
     first: { $arrayElemAt: [ "$favorites", 0 ] },
     last: { $arrayElemAt: [ "$favorites", -1 ] }
  }
}

])

推荐答案

DATAMONGO-1536 即将为 Ingalls 发布.同时你可以提供你自己的AggregationExpression来创建任何需要的操作.

DATAMONGO-1536 is about to add $arrayElemAt and other missing aggregation operators to Spring Data MongoDB for the Ingalls release. Meanwhile you can provide your own AggregationExpression to create whatever operation is needed.

对于上面的类似以下内容的技巧:

For the above something like the following does the trick:

project("name") //
  .and(context -> new BasicDBObject("$arrayElemAt", asList("$favorites", 0))).as("first")
  .and(context -> new BasicDBObject("$arrayElemAt", asList("$favorites", -1))).as("last");

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