使用MongoDB从字符串中获得截然不同的第一个单词？
要从字符串中获得不同的第一个单词，可以使用distinct()。首先让我们创建一个包含文档的集合-
> db.distinctFirstWordDemo.insertOne(
{
"_id": 100,
"StudentName":"John",
"StudentFeature": "John is a good player",
"Subject":"MongoDB"
}
);
{ "acknowledged" : true, "insertedId" : 100 }
> db.distinctFirstWordDemo.insertOne(
{
"_id": 101,
"StudentName":"Carol",
"StudentFeature": "Carol is not a good player",
"Subject":"MongoDB"
}
);
{ "acknowledged" : true, "insertedId" : 101 }在find()方法的帮助下显示集合中的所有文档-
> db.distinctFirstWordDemo.find().pretty();
这将产生以下输出-
{
"_id" : 100,
"StudentName" : "John",
"StudentFeature" : "John is a good player",
"Subject" : "MongoDB"
}
{
"_id" : 101,
"StudentName" : "Carol",
"StudentFeature" : "Carol is not a good player",
"Subject" : "MongoDB"
}以下是从字符串中获取不同的第一个单词的查询-
> student = db.distinctFirstWordDemo.distinct("StudentFeature", {"Subject" : "MongoDB"}).map(function(st){
return st.split(" ")[0];
});
[ "John", "Carol" ]
> printjson(student);这将产生以下输出-
[ "John", "Carol" ]