Question

我已阅读mongo手册3.6。它有一个例子json - bios ExampleCollection，如下所示：

final Window mRootWindow = getWindow();
        ll_main.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener(){
            public void onGlobalLayout(){
                int screenHeight = ll_main.getRootView().getHeight();
                Rect r = new Rect();
                View view = mRootWindow.getDecorView();
                view.getWindowVisibleDisplayFrame(r);

                int keyBoardHeight = screenHeight - r.bottom;
            }
        });

根据手册，要查询文档数组，QL是这样的：

{
    "_id" : 1,
    "name" : {
        "first" : "John",
        "last" : "Backus"
    },
    "birth" : ISODate("1924-12-03T05:00:00Z"),
    "death" : ISODate("2007-03-17T04:00:00Z"),
    "contribs" : [
        "Fortran",
        "ALGOL",
        "Backus-Naur Form",
        "FP"
    ],
    "awards" : [
        {
            "award" : "W.W. McDowell Award",
            "year" : 1967,
            "by" : "IEEE Computer Society"
        },
        {
            "award" : "National Medal of Science",
            "year" : 1975,
            "by" : "National Science Foundation"
        },
        {
            "award" : "Turing Award",
            "year" : 1977,
            "by" : "ACM"
        },
        {
            "award" : "Draper Prize",
            "year" : 1993,
            "by" : "National Academy of Engineering"
        }
    ]
}

我使用spring mongo模板使用上面的表达式查询此文档：

db.bios.find(
   {
      awards: {
                $elemMatch: {
                     award: "Turing Award",
                     year: { $gt: 1980 }
                }
      }
   }
)

我不明白为什么结果列表为空。我调试最后一个语句并观察查询变量。它的字符串格式是：

Query query = new Query();
query.addCriteria( Criteria.where("awards").elemMatch( 
Criteria.where("award").is("Turing Award").and("year").gt(new Integer(1980))) );
List<TestEntity> list = mongoTemplate.find(query, TestEntity.class, "testentity");
Assert.assertTrue(!list.isEmpty());
//testentity is a collection in my local db to store example json text.

并复制

Query: { "awards" : { "$elemMatch" : { "award" : "Turing Award" , "year" : { "$gt" : 1980}}}}, Fields: null, Sort: null

到robo 3T mongo客户端工具查询。它查询3个结果。 java代码如何工作？
谢谢。

Answer 1

尝试更改

{
    "award" : "Turing Award",
    "year" : 1977,
    "by" : "ACM"
},

到

 {
    "award" : "Turing Award",
    "year" : 1981,
    "by" : "ACM"
 }

用于查询文档数组的mongo模板

1 个答案: