如何按日分组核心数据? [英] how to group by day with core data?

问题描述

我有一个名为deal的实体，并且deal有一个名为date的属性，这是此交易对象插入商店的时间.

I have a Entity called deal and deal has a property called date which is the time this deal object inserted into the store.

和一天可能有几个deal.

所以我想按天计算一些数据组，我想获取day和countofsomething
像:

So I want count some data group by day, I want fetch dayand countofsomething
like:

2013-06-03 3
2013-06-02 4

，并且我不想使用sectionPath，因为它只会将交易放入分区.

and I don't want to use sectionPath because it only put deals into section.

我知道我可以通过具有另一个属性(类型:字符串)(例如dayOfTheDate)来实现此目的，该属性类似于每个对象中的2013-06-03.

I know I can have this done by have another property(type:string) like dayOfTheDate which is like 2013-06-03 in each object.

顺便说一句，瞬态属性在这种情况下似乎不起作用

btw, transient property don't seem to work in this situation

您能明白我在找什么吗?

Could you understand what I am looking for?

在这里评论，以便我提供更多详细信息

Comment here so I can provide more detail

谢谢大家.

推荐答案

计算相同笔记数时的操作方式示例

Sample of how I did it when I counted number of same notes

NSEntityDescription* entity = [NSEntityDescription entityForName:@"Assets"
                                          inManagedObjectContext:[appDelegate managedObjectContext]];
NSAttributeDescription* statusDesc = [entity.attributesByName objectForKey:@"notes"];
NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"assetUrl"]; // Does not really matter
NSExpression *countExpression = [NSExpression expressionForFunction: @"count:"
                                                          arguments: [NSArray arrayWithObject:keyPathExpression]];
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
[expressionDescription setName: @"count"];
[expressionDescription setExpression: countExpression];
[expressionDescription setExpressionResultType: NSInteger32AttributeType];
[searchFetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:statusDesc,expressionDescription, nil]];
[searchFetchRequest setPropertiesToGroupBy:[NSArray arrayWithObject:statusDesc]];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timestamp" ascending:NO];
[searchFetchRequest setSortDescriptors:@[sortDescriptor]];
[searchFetchRequest setFetchLimit:10];
NSPredicate *query = [NSPredicate predicateWithFormat:@"notes contains[cd] %@",_txtCameraNote.text];
[searchFetchRequest setPredicate:query];
[searchFetchRequest setResultType:NSDictionaryResultType];
NSArray *fetchedObjects = [appContext executeFetchRequest:searchFetchRequest error:nil];

fetchedObjects就是这样.

({
    count = 1;
    notes = "glenny and me";
},
{
    count = 6;
    notes = macair;
})

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