需要帮助进行复杂的核心数据查询

Question

我有一个名为UserProfile的表，如下所述

我需要不同的位置，计算不同的位置，并计算在user = user1的不同位置的值为0的状态。状态值可以在0 t0 5（数字）

之间

所以输出将是

abc 3 2
abd 1 1

，其中 abc 是唯一的位置， 3 是表格中abc的总计数， 2 是位置abc处状态= 0的总计数

Answer 1

我可以给你一些灵感，因为我认为，这个状态＆＃39;可能只有0或1.如果那不是真的，那么 - 我想 - 你必须用不同的谓词执行两个单独的提取（一个用于获取指向user1的位置计数，另一个用于用户的状态计数） = user1和status = 1）。

NSFetchRequest *fetchRequest =  [[NSFetchRequest alloc] init];

//create entity
NSEntityDescription *entity = [NSEntityDescription entityForName:@"UserProfile" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

//filter for user = user1
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"user == %@",user1];
[fetchRequest setPredicate:predicate];

//count of the status == 1 
NSExpressionDescription* sumStatusIsOne = [[NSExpressionDescription alloc] init];
[sumStatusIsOne setExpression:[NSExpression expressionForFunction:@"sum:"
                                            arguments:[NSArray arrayWithObject:[NSExpression expressionForKeyPath:@"status"]]]];
[sumStatusIsOne setExpressionResultType:NSDecimalAttributeType];
[sumStatusIsOne setName:@"sumStatusIsOne"];

//count of the location
NSExpressionDescription* locationCount = [[NSExpressionDescription alloc] init];
[locationCount setExpression:[NSExpression expressionForFunction:@"count:"
                                                 arguments:[NSArray arrayWithObject:[NSExpression expressionForKeyPath:@"Location"]]]
 ];
[locationCount setExpressionResultType:NSDecimalAttributeType];
[locationCount setName:@"locationCount"];

NSArray *subtractComponents = [NSArray arrayWithObjects:
                          locationCount.expression,
                          sumStatusIsOne.expression, nil];

//Count of zero status !!!Important, it is working if the 'status' can be only 1 or 0!!!
NSExpression *countOfZeroStatusExpression = [NSExpression expressionForFunction:@"from:subtract:" arguments:subtractComponents];
NSExpressionDescription* countOfZeroStatus = [[NSExpressionDescription alloc] init];
[countOfZeroStatus setExpression:countOfZeroStatusExpression];
[countOfZeroStatus setExpressionResultType:NSDecimalAttributeType];
[countOfZeroStatus setName:@"countOfZeroStatusExpression"];

[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:@"Location", locationCount,countOfZeroStatus, nil]];
[fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObject:@"Location"]];
[fetchRequest setResultType:NSDictionaryResultType ];

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

NSLog(grouppedResults);