coredata - 将一个属性提取到数组中 [英] coredata - fetch one attribute into an array

问题描述

目标：我想从数据库（核心数据）中获取一个属性的值（来自实体）到数组中。

实体名称=员工

Attribute = employeeID

我只想将所有employeeID填充到数组/集合中。

问题 / p>

下面是我的实现，我只是觉得它是一种圆的方式，我想知道是否有一个更好的方法来做这个。 >

代码

  NSFetchRequest * fetchRequest = [NSFetchRequest fetchRequestWithEntityName：@Employees]; 
 
 fetchRequest.resultType = NSDictionaryResultType; 
 
 [fetchRequest setPropertiesToFetch：[NSArray arrayWithObjects：@employeeID，nil]]; 
 
 NSError * error = nil; 
 NSArray * results = [self.managedObjectContext executeFetchRequest：fetchRequest 
 error：& error]; 
 
 NSMutableArray * employeeIDs = [NSMutableArray array]; 
 
 for（id currentRecord in results）
 {
 [employeeIDs addObject：[currentRecord objectForKey：@employeeID]]; 
} 
  

解决方案

  NSMutableArray * employeeIDs = [NSMutableArray array]; 
 
 for（id currentRecord in results）
 {
 [employeeIDs addObject：[currentRecord objectForKey：@employeeID]]; 
} 
  

尝试此操作，

  NSMutableArray * employeeIDs = [results valueForKey：@employeeID]; 
  

Aim: I would like to fetch the value of one attribute (from an entity) from the database (core data) into an array.

Example

Entity Name = Employees

Attribute = employeeID

I just want all the employeeIDs populated into an array / set.

Question

Given below is my implementation, I just feel it is kind of a round about way, I would like to know if there is a better way to do this.

Code

NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Employees"];

fetchRequest.resultType = NSDictionaryResultType;

[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:@"employeeID", nil]];

NSError *error      = nil;
NSArray *results    = [self.managedObjectContext executeFetchRequest:fetchRequest
                                                               error:&error];

NSMutableArray *employeeIDs = [NSMutableArray array];

for(id currentRecord in results)
{
    [employeeIDs addObject:[currentRecord objectForKey:@"employeeID"]];
}

解决方案

You can avoid the last for loop,

Instead of,

NSMutableArray *employeeIDs = [NSMutableArray array];

for(id currentRecord in results)
{
    [employeeIDs addObject:[currentRecord objectForKey:@"employeeID"]];
}

Try this,

NSMutableArray *employeeIDs = [results valueForKey:@"employeeID"];

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