Swift - 如何调试核心数据关系错误？

问：

我正在创建一个产品的核心数据对象，该对象还具有许多其他产品，并且具有多对多关系。

转换我的 json 时，我检查该产品是否有关联的产品，然后添加关系。

if let relatedItems = response["related"] as? [[String:Any]] {
    // create the related items
    for d in relatedItems {
        let related = try createAssociatedFromResponse(response: d)
        product.addToAssociatedProducts(related)
        try self.managedObjectContext.save()
    }
}

这会产生一个不一致的错误 - 由于未捕获的异常“NSInternalInconsistencyException”而终止应用，原因：“对象不应同时修改和添加”

我尝试检查该对象是否已经作为关系存在，但仍然收到此错误。

编辑 - 将 json 转换为核心数据对象的完整代码

func createFromResponse(response: Dictionary<String, Any>) throws -> Product {
        
        let productID = response["id"] as! NSNumber
        
        var product: Product!
        
        let fetchRequest: NSFetchRequest<Product> = Product.fetchRequest()
        fetchRequest.predicate = NSPredicate(format: "productID = %@", productID)
        
        if let fetchedProduct = try self.managedObjectContext.fetch(fetchRequest).first {
            product = fetchedProduct
        } else {
            product = (NSEntityDescription.insertNewObject(forEntityName: "Product", into: self.managedObjectContext) as! Product)
            product.productID = productID
        }
        
        product.name = response["name"] as? String
        product.ref = response["ref"] as? String
        product.desc = response["description"] as? String
        product.imageURL = response["image"] as? String
        product.image = nil
        product.thumbImageURL = response["thumb"] as? String
        product.thumbImage = nil
        product.pdfURL = response["pdf"] as? String
        product.manufacturerUrl = response["manufacturer_url"] as? String
        
        if let categoriesInHierarchy = response["categories"] as? NSArray
        {
            if categoriesInHierarchy.count == 3
            {
                if let topCategory = categoriesInHierarchy[0] as? [String:Any] {
                    product.topCategoryID = topCategory["id"] as? NSNumber
                    product.topCategoryName = topCategory["name"] as? String
                }
                
                if let subCategory = categoriesInHierarchy[1] as? [String:Any] {
                    product.subCategoryID = subCategory["id"] as? NSNumber
                    product.subCategoryName = subCategory["name"] as? String
                }
                
                if let bottomCategory = categoriesInHierarchy[2] as? [String:Any] {
                    product.bottomCategoryID = bottomCategory["id"] as? NSNumber
                    product.bottomCategoryName = bottomCategory["name"] as? String
                }
                
            }
        }
        
        if let relatedItems = response["related"] as? [[String:Any]] {
            // create the related items
            for d in relatedItems {
                let related = try createAssociatedFromResponse(response: d)
                product.addToAssociatedProducts(related)
            }
            try self.managedObjectContext.save()
        }
        
        return product
    }

func createAssociatedFromResponse(response: Dictionary<String, Any>) throws -> Product {
        
        let productID = response["id"] as! NSNumber
        
        var product: Product!
        
        let fetchRequest: NSFetchRequest<Product> = Product.fetchRequest()
        fetchRequest.predicate = NSPredicate(format: "productID = %@", productID)
        
        if let fetchedProduct = try self.managedObjectContext.fetch(fetchRequest).first {
            product = fetchedProduct
        } else {
            product = (NSEntityDescription.insertNewObject(forEntityName: "Product", into: self.managedObjectContext) as! Product)
            product.productID = productID
        }
        
        product.name = response["name"] as? String
        product.ref = response["ref"] as? String
        product.desc = response["description"] as? String
        product.imageURL = response["image"] as? String
        product.image = nil
        product.thumbImageURL = response["thumb"] as? String
        product.thumbImage = nil
        product.pdfURL = response["pdf"] as? String
        product.manufacturerUrl = response["manufacturer_url"] as? String
        
        if let categoriesInHierarchy = response["categories"] as? NSArray
        {
            if categoriesInHierarchy.count == 3
            {
                if let topCategory = categoriesInHierarchy[0] as? [String:Any] {
                    product.topCategoryID = topCategory["id"] as? NSNumber
                    product.topCategoryName = topCategory["name"] as? String
                }
                
                if let subCategory = categoriesInHierarchy[1] as? [String:Any] {
                    product.subCategoryID = subCategory["id"] as? NSNumber
                    product.subCategoryName = subCategory["name"] as? String
                }
                
                if let bottomCategory = categoriesInHierarchy[2] as? [String:Any] {
                    product.bottomCategoryID = bottomCategory["id"] as? NSNumber
                    product.bottomCategoryName = bottomCategory["name"] as? String
                }
                
            }
        }
        
        product.associatedProducts = nil
        
        return product
    }