MongoDB修改数据类型，int与字符串互转

operator_log为集合名，operation_type为字段名

{$type:2}代表type是2的，即字符串，查询所有字符串的forEach，并复制，保存

db.operator_log.find({"operation_type":{$type:2}}).forEach(function(x)
{
x.operation_type=NumberInt(x.operation_type);
db.operator_log.save(x);
}
)

db.operator_log.find({"operation_type":{$exists:true}}).forEach(function(x){
    x.operation_type=x.operation_type+"";   // 用new string(x.operation_type)就变成了文档，不知道为什么
    db.operator_log.save(x);
});