查看一个文档的一个键值comments为一个数组[“test1”,”test2”]：
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test1",
"test2"
]
}
>
一、$push向数组末尾添加元素
> db.post.update({"id":1},{$push:{"comments": "test3"}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test1",
"test2",
"test3"
]
}
>
使用$each一次性添加多个值：
> db.post.update({"id":1},{$push:{"comments":{$each:["test4","test5","test6"]}}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test1",
"test2",
"test3",
"test4",
"test5",
"test6"
]
}
>二、用$pop删除数组中的元素
从数组末尾删除一个值：
> db.post.update({"id":1},{$pop:{"comments":1}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test1",
"test2",
"test3",
"test4",
"test5"
]
}从数组开头删除一个值：
> db.post.update({"id":1},{$pop:{"comments":-1}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test2",
"test3",
"test4",
"test5"
]
}
>三、删除数组中一个指定的值：
> db.post.update({"id":1},{$pull:{"comments":"test3"}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test2",
"test4",
"test5"
]
}
>四、基于数组下标位置修改：
> db.post.update({"id":1},{$set:{"comments.1":"test9"}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.post.findOne({"id":1})
{
"_id" : ObjectId("54a530c3ff0df3732bac1680"),
"id" : 1,
"name" : "joe",
"age" : 21,
"comments" : [
"test2",
"test9",
"test5"
]
}
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