从核心数据获取多个实体的数据 [英] Fetch data from core data multiple entities

问题描述

我是 Objective-C 和核心数据的新用户。我正在做一个小项目作为我的学习的一部分。我使用产品， OrderItem ，销售和供应商。

 
产品：product- id，supplier-id，productName，category，subcategory，qty，price，minStock，frequency。 
订单：order-id，orderDate。 
 OrderItem：order-id，product-id，qty，price，total，orderDate。 
 

我已经创建了产品和 OrderItem with OrderItem 与产品相反。

 
关系目标反向
 ordersItem OrderItem  -  
 

p>

 
关系目标反向
产品订单Item 
 

我的主要问题是如何通过加入产品显示OrderItem中的有序项目：
Product-id，ProductName，OrderDate，OrderId，Qty，Price，Total

如果是正常的sql，我可以像Select product-id，productName，order-id，orderDate，qty，price，total from OrderItem o，Product p .product-id = p.product-id

使用核心数据从OrderItem获取的方法相同，可以尝试：

   - （NSMutableArray *）loadData {
 
 //通过持久数据存储从OrderItem模型获取OrderItems 
 NSManagedObjectContext * managedObjectContext = [self context]; 
 NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] initWithEntityName：@OrderItem]; 
 
 //如何从产品中获取productName 
 //关系是基于OrderItem到Product的product
 //我需要获取productName和add到下面的数组列表显示在屏幕上。 
 
 NSMutableArray * orderList = [[NSMutableArray alloc] init]; 
 
 orderList = [[managedObjectContext executeFetchRequest：fetchRequest error：nil] mutableCopy]; 
 
 return orderList; 
} 
  

我没有从一个实体显示任何问题，

我试图在产品和订单项中添加产品和订单项同时在下面的代码，但我有错误orders.orderToProd = [NSSet setWithObject：entDesc.prodToOrder];是正确的方式吗？

 
 
 
  - （IBAction）cmdAdd：（id）sender {
 
 NSManagedObjectContext * context = [self managedObjectContext]; 
 Product * entDesc = [NSEntityDescription insertNewObjectForEntityForName：@ProductinManagedObjectContext：context]; 
 
 // set产品详细信息
 entDesc.productName = self.txtName.text; 
 entDesc.category = self.txtCategory.text; 
 entDesc.qty = [NSNumber numberWithInteger：[self.txtQty.text integerValue]]; 
 
 //这里添加OrderItems的细节
 OrderItems * orders = [NSEntityDescription insertNewObjectForEntityForName：@OrderItemsinManagedObjectContext：context]; 
 orders.price = [NSNumber numberWithInteger：[self.txtprice.text integerValue]]; 
 orders.orderQty = [NSNumber numberWithInteger：[self.txtOrderQty.text integerValue]]; 
 orders.total = [NSNumber numberWithInteger：[self.txtTotal.text integerValue]]; 
 
 // orderToProd是从orderItem到Product的关系对象，prodToOrder是从Product到OrderItem的关系
 
 //我收到此行的错误。我想它期望基于数组或逗号的项目
 //请帮助
 orders.orderToProd = [NSSet setWithObject：entDesc.prodToOrder]; 
 
 
 NSError * error = nil; 
 //将对象保存到持久存储
 if（！[context save：&error]）{
 NSLog（@无法保存！％@％@，错误，[错误localizedDescription]）; 
} 
 
 
} 
 
 

解决方案>

  NSArray * orderItems = [managedObjectContext executeFetchRequest：fetchRequest error：nil]; 
  

返回 OrderItem 对象的数组，您可以使用关系访问product和order
属性，例如：

  OrderItem * oi in orderItems）{
 Product * product = oi.product; 
 Order * order = oi.order; 
 //显示product.productName，oi.qty，order.order-id，... 
} 
  

这假设您从 OrderItem 到产品之间具有产品的关系
以及从 OrderItem 到订单的关系 order 。

请注意， OrderItem 的属性 order-id，product-id 是多余的，
作为相应的产品和订单之间的关系。
（换句话说，Core Data使用关系而不是外键。）

---

问题：假设 orderToProd 是从
OrdersItem 到产品的一对一关系，将执行以下操作以在新创建的对象之间建立关系
：

  Product * entDesc = ... 
 // ... 
 OrderItems * orders = ...; 
 // ... 
 orders.orderToProd = entDesc; 
  

I am new to Objective-C and Core Data. I am working on a small project as part of my learning. I created Core Data with entities such as Product, OrderItem, Sales and Supplier.

Attributes:

Product : product-id, supplier-id, productName, category, subcategory,qty, price,minStock,frequency.
Order : order-id, orderDate.
OrderItem : order-id, product-id,qty,price, total, orderDate.

I have created relationships between Product and OrderItem with OrderItem inverse to Product.

Relationship              Destination         Inverse
ordersItem                 OrderItem           --

for OrderItem to Product:

Relationship              Destination         Inverse
product                   Product              ordersItem

My main issue is how do I display ordered items from OrderItem by joining product as: Product-id, ProductName, OrderDate, OrderId, Qty, Price, Total ?

To achieve above if it is normal sql i could run like "Select product-id, productName, order-id, orderDate, qty, price, total from OrderItem o, Product p where o.product-id=p.product-id"

The same way to fetch from OrderItem using core data i could try:

-(NSMutableArray *)loadData{

 // Fetch the OrderItems from OrderItem model through from persistent data store
NSManagedObjectContext *managedObjectContext = [self context];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"OrderItem"];

//How do i do to get productName from Product
//the relationship is based on "product" from OrderItem to Product
//I need to get productName and add to array list below to display on the screen.

NSMutableArray *orderList =[[NSMutableArray alloc]init];

orderList =[[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

return orderList; 
}

I do not have any issue displaying from one entity but my issue is from multiple entities?

Any help or advice would be appreciated?

I am trying to add Product and OrderItems at the same time in the code below but i am having error "orders.orderToProd = [NSSet setWithObject: entDesc.prodToOrder];" is it the right way ?

- (IBAction)cmdAdd:(id)sender {

    NSManagedObjectContext *context =[self managedObjectContext];
    Product *entDesc =[NSEntityDescription insertNewObjectForEntityForName:@"Product" inManagedObjectContext:context];

    //set Product details
    entDesc.productName = self.txtName.text;
    entDesc.category = self.txtCategory.text;
    entDesc.qty=[NSNumber numberWithInteger:[self.txtQty.text integerValue]];

    //add OrderItems details here
    OrderItems *orders=[NSEntityDescription insertNewObjectForEntityForName:@"OrderItems" inManagedObjectContext:context];
    orders.price=[NSNumber numberWithInteger:[self.txtprice.text integerValue]];
    orders.orderQty=[NSNumber numberWithInteger:[self.txtOrderQty.text integerValue]];
    orders.total=[NSNumber numberWithInteger:[self.txtTotal.text integerValue]];

    //orderToProd is the relationship object from orderItem to Product and prodToOrder is relationship from Product to OrderItem

    //I am getting error with this line.  I think it expects for array or comma based items
     //Please help
     orders.orderToProd = [NSSet setWithObject: entDesc.prodToOrder];


    NSError *error = nil;
    // Save the object to persistent store
    if (![context save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
    }


}

解决方案

NSArray *orderItems = [managedObjectContext executeFetchRequest:fetchRequest error:nil];

returns an array of OrderItem objects, and you can access the "product" and "order" attributes simply using the relationships, for example:

for (OrderItem *oi in orderItems) {
    Product *product = oi.product;
    Order *order = oi.order;
    // Display product.productName, oi.qty, order.order-id, ...
}

This assumes that you have a relationship product from OrderItem to Product and also a relationship order from OrderItem to Order.

Note that the attributes order-id, product-id of OrderItem are redundant, as the corresponding Product and Order is given via the relationships. (In other words, Core Data uses relationships and not "foreign keys".)

---

To your added question: Assuming that orderToProd is a "to-one" relationship from OrdersItem to Product, you would do the following to establish a relationship between the newly created objects:

Product *entDesc = ...
// ...
OrderItems *orders = ...;
// ...
orders.orderToProd = entDesc;

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