一、导出工具mongoexport

Mongodb中的mongoexport工具可以把一个collection导出成JSON格式或CSV格式的文件。可以通过参数指定导出的数据项，也可以根据指定的条件导出数据。mongoexport具体用法如下所示：

[root@localhost mongodb]# ./bin/mongoexport --help
Export MongoDB data to CSV, TSV or JSON files.

options:
  --help                    produce help message
  -v [ --verbose ]          be more verbose (include multiple times for more 
                            verbosity e.g. -vvvvv)
  --version                 print the program's version and exit
  -h [ --host ] arg         mongo host to connect to ( <set name>/s1,s2 for 
                            sets)
  --port arg                server port. Can also use --host hostname:port
  --ipv6                    enable IPv6 support (disabled by default)
  -u [ --username ] arg     username
  -p [ --password ] arg     password
  --dbpath arg              directly access mongod database files in the given 
                            path, instead of connecting to a mongod  server - 
                            needs to lock the data directory, so cannot be used
                            if a mongod is currently accessing the same path
  --directoryperdb          if dbpath specified, each db is in a separate 
                            directory
  --journal                 enable journaling
  -d [ --db ] arg           database to use
  -c [ --collection ] arg   collection to use (some commands)
  -f [ --fields ] arg       comma separated list of field names e.g. -f 
                            name,age
  --fieldFile arg           file with fields names - 1 per line
  -q [ --query ] arg        query filter, as a JSON string
  --csv                     export to csv instead of json
  -o [ --out ] arg          output file; if not specified, stdout is used
  --jsonArray               output to a json array rather than one object per 
                            line
  -k [ --slaveOk ] arg (=1) use secondaries for export if available, default 
                            true

参数说明：

-h:指明数据库宿主机的IP

-u:指明数据库的用户名

-p:指明数据库的密码

-d:指明数据库的名字

-c:指明collection的名字

-f:指明要导出那些列

-o:指明到要导出的文件名

-q:指明导出数据的过滤条件

?

实例：test库中存在着一个students集合，集合中数据如下：

> db.students.find()
{ "_id" : ObjectId("5031143350f2481577ea81e5"), "classid" : 1, "age" : 20, "name" : "kobe" }
{ "_id" : ObjectId("5031144a50f2481577ea81e6"), "classid" : 1, "age" : 23, "name" : "nash" }
{ "_id" : ObjectId("5031145a50f2481577ea81e7"), "classid" : 2, "age" : 18, "name" : "james" }
{ "_id" : ObjectId("5031146a50f2481577ea81e8"), "classid" : 2, "age" : 19, "name" : "wade" }
{ "_id" : ObjectId("5031147450f2481577ea81e9"), "classid" : 2, "age" : 19, "name" : "bosh" }
{ "_id" : ObjectId("5031148650f2481577ea81ea"), "classid" : 2, "age" : 25, "name" : "allen" }
{ "_id" : ObjectId("5031149b50f2481577ea81eb"), "classid" : 1, "age" : 19, "name" : "howard" }
{ "_id" : ObjectId("503114a750f2481577ea81ec"), "classid" : 1, "age" : 22, "name" : "paul" }
{ "_id" : ObjectId("503114cd50f2481577ea81ed"), "classid" : 2, "age" : 24, "name" : "shane" }

由上可以看出文档中存在着3个字段：classid、age、name

1.直接导出数据到文件中

[root@localhost mongodb]# ./bin/mongoexport -d test -c students -o students.dat
connected to: 127.0.0.1
exported 9 records

命令执行完后使用ll命令查看