如何在Swift中实现可动态添加过滤条件的Firestore查询？

Firestore Swift SDK中的Query为不可变结构体，每次调用whereField、order、limit等条件拼接方法都会生成全新的Query实例，只要将新实例赋值回原有变量即可实现动态拼接查询条件的需求，你的整体逻辑完全正确，仅存在两处细节错误导致逻辑不生效：

1. 排序和条数限制的方法返回的新Query没有赋值回原变量，修改不生效
2. 代码中存在两处笔误，错误将self.lbl_field.text、self.lbl_duration.text写为了cell.lbl_field.text、cell.lbl_duration.text，导致条件取值错误

var query = db.collection("admissions")
// 搜索关键词条件
if (self.txt_search.text?.count ?? 0 > 0) {
    query = query.whereField("keyword", arrayContains: self.txt_search.text ?? "")
}
// 州/省筛选条件
if(self.lbl_state.text != "State" && self.lbl_state.text != "" && self.lbl_state.text != "Any") {
    query = query.whereField("state", isEqualTo: self.lbl_state.text ?? "")
}
// 学历等级筛选条件
if(self.lbl_level.text != "Level" && self.lbl_level.text != "" && self.lbl_level.text != "Any") {
    query = query.whereField("type", isEqualTo: self.lbl_level.text ?? "")
}
// 专业领域筛选条件
if(self.lbl_field.text != "Field" && self.lbl_field.text != "" && self.lbl_field.text != "Any") {
    // 修复笔误：从self取值而非cell
    query = query.whereField("field_broad", isEqualTo: self.lbl_field.text ?? "")
}
// 院校筛选条件
if(self.lbl_provider.text != "Provider" && self.lbl_provider.text != "" && !self.selectedUniversity.contains("Any")) {
    query = query.whereField("university", in: self.selectedUniversity)
}
// 学制筛选条件
if(self.lbl_duration.text != "Duration" && self.lbl_duration.text != "" && self.lbl_duration.text != "Any") {
    // 修复笔误：从self取值而非cell
    if(self.lbl_duration.text == "<1 year") {
        query = query.whereField("duration", isLessThanOrEqualTo: 365)
    } else if(self.lbl_duration.text == "1-2 year") {
        query = query.whereField("duration", isGreaterThanOrEqualTo: 365).whereField("duration", isLessThanOrEqualTo: 365 * 2)
    } else {
        query = query.whereField("duration", isGreaterThanOrEqualTo: 365 * 2)
    }
}
// 修复：排序和分页结果赋值回query
query = query.order(by: "duration").order(by: "id").limit(to: 50)

// 执行查询
query.getDocuments() { (querySnapshot, err) in
    AFWrapper.stopAnimating()
    if let err = err {
        print("Error getting documents: \(err)")
    } else {
        for document in querySnapshot!.documents {
            print("\(document.documentID) => \(document.data())")
        }   
    }
}

可以把重复的参数合法性判断抽成单独的工具方法，减少冗余代码，示例如下：

func isValidFilterParam(_ value: String?, placeholder: String) -> Bool {
    guard let value = value, !value.isEmpty else { return false }
    return value != placeholder && value != "Any"
}

// 调用示例
if isValidFilterParam(self.lbl_state.text, placeholder: "State") {
    query = query.whereField("state", isEqualTo: self.lbl_state.text ?? "")
}

内容的提问来源于stack exchange，提问作者Guri