英文:
How to build mgo queries?
问题
我正在使用revel和mgo做一个小项目（练习），但是在构建查询时，搜索功能出了一些问题。代码看起来像这样：
conditions := make(bson.M, 0)conditions["status"] = bson.M{"$ne": "delete"}if item, ok := paramsPost["title"]; ok {if item[0] != "" {conditions["title"] = bson.RegEx{Pattern: item[0]}}}if item, ok := paramsPost["from_date"]; ok {if item[0] != "" {conditions["publishdate"] = bson.M{}fromDate, _ := time.Parse("2006-01-02", item[0])conditions["publishdate"]["$gte"] = fromDate.Unix()}}if item, ok := paramsPost["to_date"]; ok {if _, ok := conditions["publishdate"]; !ok {conditions["publishdate"] = bson.M{}}if item[0] != "" {toDate, _ := time.Parse("2006-01-02", item[0])conditions["publishdate"]["$lte"] = toDate.Unix()}}
然后我得到了一些错误信息：
invalid operation: conditions["publishdate"]["$gte"] (index of type interface {})
我知道我做错了什么，但是我不知道为什么，也不知道如何解决。有人可以帮助我吗？谢谢。
英文:
I'm doing a tiny project(practice) with revel and mgo, but I got something wrong with search function when I build the queries. The code seems like this:
conditions := make(bson.M, 0)conditions["status"] = bson.M{"$ne": "delete"}if item, ok := paramsPost["title"]; ok {if item[0] != "" {conditions["title"] = bson.RegEx{Pattern: item[0]}}}if item, ok := paramsPost["from_date"]; ok {if item[0] != "" {conditions["publishdate"] = bson.M{}fromDate, _ := time.Parse("2006-01-02", item[0])conditions["publishdate"]["$gte"] = fromDate.Unix()}}if item, ok := paramsPost["to_date"]; ok {if _, ok := conditions["publishdate"]; !ok {conditions["publishdate"] = bson.M{}}if item[0] != "" {toDate, _ := time.Parse("2006-01-02", item[0])conditions["publishdate"]["$lte"] = toDate.Unix()}}
And I got some error info:
invalid operation: conditions["publishdate"]["$gte"] (index of type interface {})
I know I make something wrong, but I don't know why, and how to resolve. Anybody can help me? Thanks
答案1
得分: 4
bson.M 是一个 map[string]interface{} 类型的变量（http://godoc.org/labix.org/v2/mgo/bson#M）。
所以，在以下代码中：
conditions["publishdate"]["$gte"] = fromDate.Unix()
当在 map 中查找 publishdate 时，你需要将 interface{} 类型断言为 bson.M 类型。
相反，你可以重构代码，改为以下形式：
publishdate := bson.M{}// ... 在这里添加你的逻辑conditions["publishdate"] = publishDate
这样可以避免不必要的 map 查找和类型断言。
英文:
bson.M is a map[string]interface{} (http://godoc.org/labix.org/v2/mgo/bson#M)
So, in
conditions["publishdate"]["$gte"] = fromDate.Unix()
You need to do a type assertion from interface{} to bson.M when looking up publishdate in the map.
Instead, you could refactor the code to something like
publishdate:= bson.M{}// ... your logic goes hereconditions["publishdate"] = publishDate
to save on unnecessary map lookups and type assertions.
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