I tried to iterate backwards with using a Range and each: (4..0).each do |i| puts i end ==> 4..0 Iteration through 0..4 writes the numbers. On the other Range r = 4..0 seems to be ok, r.first ==
目录导出数据mongodumpmongoexport恢复mongorestoremongoimport需要提前安装MongoDB-database-tools参考：Centos离线安装mongodb-database-tools
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