从 1 table w.r.t table 2 过滤数据的领域子查询

Question

假设我在 Realm 数据库中有两个模型和对应的表

public class Customer :Object {
   dynamic var  Id : String = ""
   dynamic var  NAME : String = ""
   dynamic var  Address : String = ""

   override public class func primaryKey() -> String? {
      return "Id"
   }  
}


public class Bills :Object {
    dynamic var  Id : String = ""
    dynamic var  Amount : String = ""
    dynamic var  CustomerId : String = ""

    override public class func primaryKey() -> String? {
        return "Id"
    }
}

What I am doing: I am getting list of All customers easily by doing this

realmObj.objects(Customer.self)

What I want: I want to do followings.

我想获取所有客户列表，但我还希望该列表包含最常购买商品的客户。我的意思是我希望根据从我们商店购买更多时间的客户来订购清单。为此，我可以从 Bills 表中的客户 ID 中获取它。但是我不知道如何在Realm中做到这一点。

我知道可以通过子查询来完成，但我不知道如何在 Realm 中进行。请告诉我这里 query/Predicate 是什么以获得所需的结果。

Answer 1

我有两个答案，但有几件事需要先解决。

对于你的两个 classes，如果你希望它们由 Realm 管理，你需要在每个你想要管理的变量之前包含 @objc

public class Customer :Object {
   @objc dynamic var  Id : String = ""

或选择性地将@objcMembers 添加到 class 名称

@objcMembers class Customer :Object {
       dynamic var  Id : String = ""

另一件事是 class 属性 (vars) 应始终为小写，class 名称应以大写开头。什么都不应该全部大写。

public class Customer :Object {
   @objc dynamic var  customer_id : String = ""
   @objc dynamic var  name : String = ""

第一个解决方案是使用您当前的结构：

var topCustomers = [(String, Int)]() //stores the customer id and count in an array of tuples
let results = realm.objects(Bills.self) //get all the bills
let allCustomerIds = results.map{ [=13=].CustomerId } //get a list of all of the customer id's
let uniqueIds = Set(allCustomerIds) //create a set of unique customer ids

for custId in uniqueIds { //iterate over the array of unique customer id's
    let count = results.filter("CustomerId == %@", custId).count // get a count of each customer id from results
    topCustomers.append( (custId, count) ) //add the customer id and it's count to the array
}

topCustomers.sort { [=13=].1 > .1 } //sort the array by count
for x in topCustomers { //print out the array - the customer with the most bills will be at the top
    print(x.0, x.1)
}

第二种更优雅的方法使用客户与其账单之间的关系。这将为生成报告、查询和整体组织提供更大的灵活性。

这是更新后的 classes:

class CustomerClass: Object {
   @objc dynamic var  customer_id = UUID().uuidString
   @objc dynamic var  name = ""
   @objc dynamic var  address = ""

   let billList = List<BillClass>()

   override public class func primaryKey() -> String? {
      return "customer_id"
   }
}

class BillClass: Object {
    @objc dynamic var  bill_id = UUID().uuidString
    @objc dynamic var  amount = ""

    override public class func primaryKey() -> String? {
        return "bill_id"
    }
}

然后是一些非常短的代码来完成与第一个示例相同的事情

let customers = realm.objects(CustomerClass.self) //get all customers
let results = customers.map { ([=15=].name, [=15=].billList.count) } //iterate over all, creating tuple with customer name & bill count
let sortedResults = results.sorted(by: { [=15=].1 > .1} ) //sort by bill count, descending
sortedResults.forEach { print([=15=]) } //print the results, customer will most bills at top

注意UUID().uuidString的使用

@objc dynamic var  bill_id = UUID().uuidString

为您的对象创建唯一的主键。消除处理索引、唯一性、递增等。

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ios

swift

xcode

realm

realm-mobile-platform