mongodb 怎么实现类似 case when then

mongodb 怎么实现类似 case when then

mongodb中使用 $cond条件来完成类似case when then的功能。
node.js参考代码
exports.sumByGSAsync = function (opts) {
var results = {error_code: -1, error_msg: "error"};
var beginDate=opts.beginDate;
var endDate=opts.endDate;
var pipeline =[
{
$match: {
sjbh: {$gte: beginDate, $lte:endDate}
}
},
{
$group: {
_id: "$gsbh",
totaltxl: {$sum: { $cond: { if: { $ne: [ "$totalnum","" ] }, then:"$txl" , else: 0 }}},
totalbmynum: {$sum: "$bmynum"}
}
},
{
$project: {
_id: 0,
gsbh: "$_id",
totaltxl: "$totaltxl",
totalbmynum: "$totalbmynum",
ratio: { $divide: [ "$totalbmynum", { $cond:{if: { $eq: [ "$totaltxl",0 ] }, then:1 , else: "$totaltxl" }}] }
}
},
{$sort: {ratio: -1}}
];

return opts.dbs.csdb.collection("permydfx").aggregateAsync(pipeline)
.timeout(opts.configs.timeoutnormal)
.then(function (value) {
.....
});
}