前言
此篇博文是 Mongdb 基础系列之一；
本文为作者的原创作品，转载需注明出处；
Command Line Help
1 | $ mongo --help |
将打印出如下的信息，
1 | MongoDB shell version v3.4.6 |
Shell Help
在 mongo shell 中输入如下指令，
1 | > help |
将输出如下的信息，
1 | db.help() help on db methods |
Database Help
在 mongo shell 中通过如下指令获得有关 Database 的帮助信息，
获得当前所有 available 的 databases
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> show dbs
New in version 2.4: show databases is now an alias for show dbs
To see the list of help for methods you can use on the db object, call the db.help() method:
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> db.help()
将会所有相关的 db 方法集
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13DB methods:
db.adminCommand(nameOrDocument) - switches to 'admin' db, and runs command [ just calls db.runCommand(...) ]
db.auth(username, password)
db.cloneDatabase(fromhost)
db.commandHelp(name) returns the help for the command
db.copyDatabase(fromdb, todb, fromhost)
db.createCollection(name, { size : ..., capped : ..., max : ... } )
db.createView(name, viewOn, [ { $operator: {...}}, ... ], { viewOptions } )
db.createUser(userDocument)
db.currentOp() displays currently executing operations in the db
db.dropDatabase()
db.eval() - deprecated
......To see the
implementationof a method in the shell, type thedb.<method name>without the parenthesis (()), as in the following example which will return the implementation of the method db.updateUser():1
> db.updateUser
将返回 updateUser() 的具体实现；
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18function (name, updateObject, writeConcern) {
var cmdObj = {updateUser: name};
cmdObj = Object.extend(cmdObj, updateObject);
cmdObj['writeConcern'] = writeConcern ? writeConcern : _defaultWriteConcern;
this._modifyCommandToDigestPasswordIfNecessary(cmdObj, name);
var res = this.runCommand(cmdObj);
if (res.ok) {
return;
}
if (res.errmsg == "no such cmd: updateUser") {
this._updateUserV1(name, updateObject, cmdObj['writeConcern']);
return;
}
throw _getErrorWithCode(res, "Updating user failed: " + res.errmsg);
}
Collection Help
在 mongo shell 中执行，
查看当前 database 中所有的 collections
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> show collections
在我本地的测试如下，
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5> use local
switched to db local
> show collections
startup_log
>查看某一个 collection 上的可用方法，直接在该 collection 上调用 help()
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> db.collection.help()
在我本地的测试如下，
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10> db.startup_log.help()
DBCollection help
db.startup_log.find().help() - show DBCursor help
db.startup_log.bulkWrite( operations, <optional params> ) - bulk execute write operations, optional parameters are: w, wtimeout, j
db.startup_log.count( query = {}, <optional params> ) - count the number of documents that matches the query, optional parameters are: limit, skip, hint, maxTimeMS
db.startup_log.copyTo(newColl) - duplicates collection by copying all documents to newColl; no indexes are copied.
db.startup_log.convertToCapped(maxBytes) - calls {convertToCapped:'startup_log', size:maxBytes}} command
db.startup_log.createIndex(keypattern[,options])
db.startup_log.createIndexes([keypatterns], <options>)
db.startup_log.dataSize()查看某一个 collection 对应的方法的实现，使用
db.<collection>.<method>namewithoutthe parenthesis (())1
> db.collection.save
在我本地的测试如下，
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4> db.startup_log.dataSize
function () {
return this.stats().size;
}
Cursor Help
When you perform read operations with the find() method in the mongo shell, you can use various cursor methods to modify the find() behavior and various JavaScript methods to handle the cursor returned from the find() method.
在执行读取操作的时候，你可以使用多种多样的 cursor 方法来修改 find() 方法的行为以及处理 find() 方法的返回方式；
To list the available modifier and cursor handling methods, use the db.collection.find().help() command
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> db.collection.find().help()
在我本地的测试如下，
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36> db.startup_log.find().help()
find(<predicate>, <projection>) modifiers
.sort({...})
.limit(<n>)
.skip(<n>)
.batchSize(<n>) - sets the number of docs to return per getMore
.collation({...})
.hint({...})
.readConcern(<level>)
.readPref(<mode>, <tagset>)
.count(<applySkipLimit>) - total # of objects matching query. by default ignores skip,limit
.size() - total # of objects cursor would return, honors skip,limit
.explain(<verbosity>) - accepted verbosities are {'queryPlanner', 'executionStats', 'allPlansExecution'}
.min({...})
.max({...})
.maxScan(<n>)
.maxTimeMS(<n>)
.comment(<comment>)
.snapshot()
.tailable(<isAwaitData>)
.noCursorTimeout()
.allowPartialResults()
.returnKey()
.showRecordId() - adds a $recordId field to each returned object
Cursor methods
.toArray() - iterates through docs and returns an array of the results
.forEach(<func>)
.map(<func>)
.hasNext()
.next()
.close()
.objsLeftInBatch() - returns count of docs left in current batch (when exhausted, a new getMore will be issued)
.itcount() - iterates through documents and counts them
.getQueryPlan() - get query plans associated with shape. To get more info on query plans, call getQueryPlan().help().
.pretty() - pretty print each document, possibly over multiple linesTo see the
implementationof the cursor method, type thedb.<collection>.find().<method>name without the parenthesis (()), as in the following example which will return the implementation of the toArray() method:1
> db.collection.find().toArray
Some useful methods for handling cursors are:
- hasNext() which checks whether the cursor has more documents to return.
- next() which returns the next document and advances the cursor position forward by one.
- forEach(
) which iterates the whole cursor and applies the<function>to each document returned by the cursor. The<function>expects a single argument which corresponds to the document from each iteration.
For examples on iterating a cursor and retrieving the documents from the cursor, see cursor handling. See also Cursor for all available cursor methods.
Wrapper Object Help
通过 help misc 在 mongo shell 中查询得到所有可用的对象( wrapped class )；
1 | > help misc |
返回
1 | b = new BinData(subtype,base64str) create a BSON BinData value |
可见，返回的都是 mongo shell 中内置的可用的 Classes 对象，以及相关的调用方法；
References
https://docs.mongodb.com/manual/tutorial/access-mongo-shell-help/