mgo 查询构建：处理嵌套 bson.M 的最佳实践与常见陷阱

import "gopkg.in/mgo.v2/bson"

// 查询 status 不为 "delete" 的文档
conditions := bson.M{
    "status": bson.M{"$ne": "delete"},
}

import (
    "time"
    "gopkg.in/mgo.v2/bson"
)

// 假设 paramsPost 是一个 map[string][]string 存储表单提交的参数
func buildQuery(paramsPost map[string][]string) bson.M {
    conditions := make(bson.M)
    conditions["status"] = bson.M{"$ne": "delete"}

    // 标题模糊查询
    if item, ok := paramsPost["title"]; ok && item[0] != "" {
        conditions["title"] = bson.RegEx{Pattern: item[0]}
    }

    // 日期范围查询的尝试
    if item, ok := paramsPost["from_date"]; ok && item[0] != "" {
        conditions["publishdate"] = bson.M{} // 问题所在：这里将 publishdate 设置为 interface{} 类型的空 map
        fromDate, _ := time.Parse("2006-01-02", item[0])
        conditions["publishdate"]["$gte"] = fromDate.Unix() // 错误发生在这里
    }

    if item, ok := paramsPost["to_date"]; ok && item[0] != "" {
        // 如果 from_date 没有设置，则需要先初始化 publishdate
        if _, ok := conditions["publishdate"]; !ok {
            conditions["publishdate"] = bson.M{}
        }
        toDate, _ := time.Parse("2006-01-02", item[0])
        conditions["publishdate"]["$lte"] = toDate.Unix()
    }
    return conditions
}

invalid operation: conditions["publishdate"]["$gte"] (index of type interface {})

import (
    "time"
    "gopkg.in/mgo.v2/bson"
)

// 假设 paramsPost 是一个 map[string][]string 存储表单提交的参数
func buildQueryCorrectly(paramsPost map[string][]string) bson.M {
    conditions := make(bson.M)
    conditions["status"] = bson.M{"$ne": "delete"}

    // 标题模糊查询
    if item, ok := paramsPost["title"]; ok && item[0] != "" {
        conditions["title"] = bson.RegEx{Pattern: item[0]}
    }

    // 独立构建 publishdate 的条件
    publishDateConditions := bson.M{} // 创建一个独立的 bson.M 来存储日期条件

    if item, ok := paramsPost["from_date"]; ok && item[0] != "" {
        fromDate, err := time.Parse("2006-01-02", item[0])
        if err == nil { // 确保日期解析成功
            publishDateConditions["$gte"] = fromDate.Unix()
        }
    }

    if item, ok := paramsPost["to_date"]; ok && item[0] != "" {
        toDate, err := time.Parse("2006-01-02", item[0])
        if err == nil { // 确保日期解析成功
            // 截止日期通常包含当天，所以将其设置为当天的最后一秒
            // 或者根据实际需求决定是 toDate.Unix() 还是 toDate.Add(24*time.Hour).Unix() - 1
            publishDateConditions["$lte"] = toDate.Unix() 
        }
    }

    // 如果 publishDateConditions 不为空，则将其添加到主 conditions
    if len(publishDateConditions) > 0 {
        conditions["publishdate"] = publishDateConditions
    }

    return conditions
}

package main

import (
    "fmt"
    "time"
    "gopkg.in/mgo.v2/bson"
)

// 模拟表单提交的参数
type FormData struct {
    Title    string
    Category string
    Status   string
    FromDate string
    ToDate   string
}

func buildDynamicQuery(data FormData) bson.M {
    query := make(bson.M)

    // 1. 默认条件：状态不为 "delete"
    query["status"] = bson.M{"$ne": "delete"}

    // 2. 标题模糊匹配
    if data.Title != "" {
        query["title"] = bson.RegEx{Pattern: data.Title, Options: "i"} // "i" 表示不区分大小写
    }

    // 3. 精确匹配分类
    if data.Category != "" {
        query["category"] = data.Category
    }

    // 4. 日期范围查询 (嵌套条件)
    publishDateConditions := bson.M{}

    if data.FromDate != "" {
        if fromDate, err := time.Parse("2006-01-02", data.FromDate); err == nil {
            publishDateConditions["$gte"] = fromDate.Unix()
        } else {
            fmt.Printf("Warning: Invalid from_date format: %s\n", data.FromDate)
        }
    }

    if data.ToDate != "" {
        if toDate, err := time.Parse("2006-01-02", data.ToDate); err == nil {
            // 通常截止日期需要包含当天，所以将其设置为当天的最后一秒
            // 或者根据业务需求决定，这里简单使用 Unix 时间戳
            publishDateConditions["$lte"] = toDate.Add(24*time.Hour - 1*time.Second).Unix()
        } else {
            fmt.Printf("Warning: Invalid to_date format: %s\n", data.ToDate)
        }
    }

    // 如果有日期条件，则添加到主查询
    if len(publishDateConditions) > 0 {
        query["publishdate"] = publishDateConditions
    }

    return query
}

func main() {
    // 示例用法
    formData1 := FormData{
        Title:    "GoLang",
        FromDate: "2023-01-01",
        ToDate:   "2023-12-31",
        Category: "Programming",
    }
    query1 := buildDynamicQuery(formData1)
    fmt.Printf("Query 1: %+v\n", query1)

    formData2 := FormData{
        Status:   "active",
        ToDate:   "2023-06-15",
    }
    query2 := buildDynamicQuery(formData2)
    fmt.Printf("Query 2: %+v\n", query2)
}

Query 1: map[category:Programming publishdate:map[$gte:1672502400 $lte:1704067199] status:map[$ne:delete] title:{Pattern:GoLang Options:i}]
Query 2: map[publishdate:map[$lte:1686854399] status:map[$ne:delete]]