swift - 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 Realm Product 和 ProductType 中有两个实体。产品与产品类型具有一对多关系。

产品实体一对多

import Foundation
import RealmSwift

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

ProductType 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包含 ProductType typeName 的产品，例如“Electronics”。如果有这样的一对一关系，我可以轻松做到这一点

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)

关于如何使用一对多版本的 Product 类进行查询有什么想法吗？

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的计数是否大于 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