SwiftUI - 在 FetchRequest 中包含关系信息

Question

我有一个与 Accounts 实体具有一对多关系的 Expense 实体。

我当前的获取请求如下：

let request = NSFetchRequest<NSFetchRequestResult>(entityName: Expenses.entity().name ?? "Expenses")     
        
request.predicate = predicate
request.returnsObjectsAsFaults = false
request.resultType = .dictionaryResultType
let expression = NSExpressionDescription()
// check operations list from apple or nshipster in nsexpressions
expression.expression =  NSExpression(forFunction: "noindex:", arguments:[NSExpression(forKeyPath: "originAccounts.isCredit")])
expression.name = "checkIsCredit"
expression.expressionResultType = .booleanAttributeType // might be another
        
let expression1 = NSExpressionDescription()
expression1.expression = NSExpression(forFunction: "noindex:", arguments:[NSExpression(forKeyPath: "id")])
expression1.name = "checkExpenses"
expression.expressionResultType = .UUIDAttributeType
        
request.propertiesToFetch = [expression,expression1]

context.perform {
    do {
        let results = try request.execute()
        print(results)

我的谓词是：

predicate: NSPredicate(format: "expenseDate >= %@ AND expenseDate < %@", datesView.prevMonthPayStart as NSDate, datesView.nextPaydate as NSDate)

当我打印我得到的结果时

[{
    expenseAccount = "Test Account";
    expenseCategory = "Test Category";
    expenseCost = 123;
    expenseDate = "2020-11-12 05:00:00 +0000";
    expenseIsPaid = 1;
    expenseName = Test;
    expenseType = "One-time";
    id = "AFB5EB0E-20A2-47EA-8F36-22D07571C213";
    shouldDupe = 1;
}, {
    expenseAccount = "Test Account";
    expenseCategory = "Test Category";
    expenseCost = 23;
    expenseDate = "2020-11-13 05:00:00 +0000";
    expenseIsPaid = 0;
    expenseName = "Test Recurring";
    expenseType = Monthly;
    id = "5CFB5E58-4377-40DA-9C6A-AF8027ACEC60";
    shouldDupe = 1;
}]

我知道我不会看到 nil 的属性，但我想通过 originAccounts 关系获取属性。这可能吗？具体来说，我想获取 originAccounts.isCredit 的值。这是一个示例对象供参考。

<Expenses: 0x60000321af80> (entity: Expenses; id: 0xa7ab05bb9341bf4a <x-coredata://ED302202-3018-445F-8FFE-DD2E85219E64/Expenses/p1>; data: {
    expenseAccount = "Test Account";
    expenseCategory = "Test Category";
    expenseCost = 123;
    expenseDate = "2020-11-12 05:00:00 +0000";
    expenseId = nil;
    expenseIsPaid = 1;
    expenseName = Test;
    expenseType = "One-time";
    id = "AFB5EB0E-20A2-47EA-8F36-22D07571C213";
    lastMonthlyExpenseID = nil;
    nextMonthlyExpenseID = nil;
    originAccounts = "0xa7ab05bb9341bf4e <x-coredata://ED302202-3018-445F-8FFE-DD2E85219E64/Accounts/p1>";
    originCategories = nil;
    shouldDupe = 1;
})

Answer 1

你能不能试试 NSExpressions，你不会获取，所以你会很高效。

    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "yourEntity")
    fetchRequest.predicate = NSPredicate(format: "yourPredicate")
    fetchRequest.resultType = .dictionaryResultType
    fetchRequest.returnsObjectsAsFaults = false
    
    let expression = NSExpressionDescription()
    // check operations list from apple or nshipster in nsexpressions
    expression.expression =  NSExpression(forFunction: "yourOperation", arguments:[NSExpression(forKeyPath: "Expenses.originAccounts.isCredit")])
    expression.name = "yourName"
    expression.expressionResultType = .decimalAttributeType // might be another
    
    fetchRequest.propertiesToFetch = [expression]
    
    do {
        let results = try viewContext.fetch(fetchRequest)
        print(results)
    } catch {
        print("Failed to fetch aggregates")
    }
}