Realm Swift 选择与一对多关系实体中的一个字段匹配的所有值

Question

我在领域产品和产品类型中有两个实体。产品与产品类型有一对多关系。

产品实体一对多

import Foundation
import RealmSwift
class Product: Object{
dynamic var productName = ""
let productTypeList = List<ProductType>() 
}

产品类型实体

import Foundation
import RealmSwift
class ProductType: Object{   
dynamic var typeName: String = ""
dynamic var typeLogoUrl: String = ""
}

我的目标是选择所有产品，其中包含产品类型名称，例如"电子产品"。我可以很容易地做到，如果有这样的一对一关系

产品实体一对一

import Foundation
import RealmSwift
class Product:Object{
dynamic var productName = ""
dynamic var productType : ProductType? 
}

查询示例

let realm = try! Realm()
let productTypeName = "Electronics"
let predicate = NSPredicate(format: "productType.typeName == %@", productTypeName)
let rmProducts = realm.objects(Product.self).filter(predicate)

任何想法如何使用产品类的一对多版本进行查询？

Answer 1

您可以使用子查询并检查列表中与名称匹配的产品类型计数是否大于 0。

let rmProducts = realm.objects(Product.self).filter("SUBQUERY(productTypeList, $type, $type.typeName == %@).@count>0",productTypeName)

我已经在以下测试集上运行了查询并得到了预期的结果：

class Product:Object{
dynamic var productName = ""
var productTypeList = List<ProductType>()
}
class ProductType  : Object{
dynamic var typeName: String = ""
dynamic var typeLogoUrl: String = ""
}
let types = [ProductType(value: ["typeName":"Electronics","typeLogoUrl":"url"]),ProductType(value: ["typeName":"a","typeLogoUrl":"url"]),ProductType(value: ["typeName":"Electronics","typeLogoUrl":"a"]),ProductType(value: ["typeName":"b","typeLogoUrl":"url"])]
let prod1 = Product()
prod1.productName = "a"
prod1.productTypeList = List([types[0],types[1]])
let prod2 = Product()
prod2.productName = "b"
prod2.productTypeList = List([types[3],types[1]])
let prod3 = Product()
prod3.productName = "c"
prod3.productTypeList = List([types[2],types[1]])
var prod4 = Product()
prod4.productName = "d"
prod4.productTypeList = List([types[1]])
try! realm.write {
realm.add(types)
realm.add([prod1,prod2,prod3,prod4])
}
let productTypeName = "Electronics"
let predicate = NSPredicate(format: "productType.typeName == %@", productTypeName)
let rmProducts = realm.objects(Product.self).filter("SUBQUERY(productTypeList, $type, $type.typeName == %@).@count>0",productTypeName)
print(rmProducts) //rmProducts contains prod1 and prod3 as expected

Answer 2

对于这样的简单查询，您需要ANY修饰符：

realm.objects(Product.self).filter("ANY productTypeList.typeName == %@", productTypeName)

SUBQUERY，如另一个答案中所建议的，仅当您需要对每个子对象进行多个条件匹配时才需要。例如，如果您想查找具有给定类型的项目且 URL 以https://开头的Products，您可以使用SUBQUERY：

realm.objects(Product.self).filter("SUBQUERY(productTypeList, $type, $type.typeName == %@ AND $type.typeLogoUrl BEGINSWITH 'https://').@count > 0", productTypeName)