Question

我有文件中的货物，我希望将文件中每种商品的数量和价格相乘并加以总结。

在mySQL中是这样的：SELECT SUM(price * quantity) FROM documentGoods

这是我的代码，但它不起作用。

NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
[fetch setEntity:[NSEntityDescription entityForName:self.tableName inManagedObjectContext:moc]];
[fetch setResultType:NSDictionaryResultType];

NSExpression *multiplyExpression = [NSExpression expressionForFunction:@"multiply:by:" arguments:@[[NSExpression expressionForKeyPath:@"quantity"], [NSExpression expressionForKeyPath:@"price"]]];
NSExpressionDescription *expressionMultipliedDescription = [[NSExpressionDescription alloc] init];
[expressionMultipliedDescription setName:@"multiplied"];
[expressionMultipliedDescription setExpression:multiplyExpression];
[expressionMultipliedDescription setExpressionResultType:NSDecimalAttributeType];

NSExpression *sumExpression = [NSExpression expressionForFunction:@"sum:" arguments:@[[NSExpression expressionForKeyPath:@"multiplied"]]];
NSExpressionDescription *expressionSummaryDescription = [[NSExpressionDescription alloc] init];
[expressionSummaryDescription setName:@"summary"];
[expressionSummaryDescription setExpression:sumExpression];
[expressionSummaryDescription setExpressionResultType:NSDecimalAttributeType];

[fetch setPropertiesToFetch:@[expressionSummaryDescription]];
NSPredicate *searchFilter = [NSCompoundPredicate andPredicateWithSubpredicates:@[[NSPredicate predicateWithFormat:@"removed = NO"]]];
[fetch setPredicate:searchFilter];
NSError *error = nil;
NSArray *objects = [moc executeFetchRequest:fetch error:&error];
if(objects && [objects count] > 0)
    return [[objects objectAtIndex:0] valueForKey:@"summary"];
return [[NSDecimalNumber alloc] initWithFloat:.0f];

有人可以帮助我吗？

Answer 1

我遇到了类似的情况，我的实体是＆＃34; Cart＆＃34;并具有字段价格和数量。为了从购物车获得总和（数量*价格），我使用了以下代码。最后一个NSLog将记录所需的总购物车价格

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

request.entity = [NSEntityDescription entityForName:@"Cart" inManagedObjectContext:self.managedObjectContext];
request.resultType = NSDictionaryResultType;

NSExpressionDescription *productTotalDescr = [[NSExpressionDescription alloc] init];
[productTotalDescr setName:@"productTotal"];
[productTotalDescr setExpression:[NSExpression expressionForFunction:@"multiply:by:"
                                                    arguments:[NSArray arrayWithObjects:
                                                               [NSExpression expressionForKeyPath:@"price"],
                                                               [NSExpression expressionForKeyPath:@"quantity"],
                                                               nil]]];
[productTotalDescr setExpressionResultType:NSInteger64AttributeType];

request.propertiesToFetch = [NSArray arrayWithObjects:productTotalDescr, nil];

NSError *err = nil;
NSArray *results = [self.managedObjectContext executeFetchRequest:request error:&err];
NSLog(@"%@",[results valueForKeyPath:@"productTotal"]);

如何将两列相乘并在CoreData中求和？

1 个答案: