使用FMDB获取复杂数据

Question

我在iOS应用程序中使用SQLite,我使用FMDB作为包装器.这是我的数据库架构:

CREATE TABLE Offer (code TEXT PRIMARY KEY NOT NULL, name TEXT);

CREATE TABLE OffreMarket (codeOffer TEXT NOT NULL,
codeMarket TEXT NOT NULL,
FOREIGN KEY(codeOffer) REFERENCES Offer(code),
FOREIGN KEY(codeMarket) REFERENCES Market(code));

CREATE TABLE Market (code TEXT PRIMARY KEY NOT NULL, name TEXT);

我的模型对象:

@interface Offer : NSObject
@property (nonatomic,copy) NSString *code;
@property (nonatomic,copy) NSString *name;
@property (nonatomic,copy) NSArray *markets;
@end

@interface OffreMarket : NSObject
@property (nonatomic,copy) NSString *codeOffer;
@property (nonatomic,copy) NSString *codeMarket;
@end

@interface Market : NSObject
@property (nonatomic,copy) NSString *code;
@property (nonatomic,copy) NSString *name;
@end

例如,我正在获取数据库中的所有商品,如下所示:

- (NSArray *)offers {
// Open database

NSMutableArray *offers = [NSMutableArray new];

FMResultSet *resultSet = [database executeQuery:@"SELECT * FROM Offer"];
while ([resultSet next]){

   Offer *offer = [Offer new];
   offer.code = [resultSet stringForKey:@"code"];
   offer.name = [resultSet stringForKey:@"name"];

   // Get the markets for each offer
   FMResultSet *marketResultSet = [database executeQuery:@"SELECT * FROM  OffreMarket WHERE codeOffer = ?",offer.code];

   NSMutableArray *offers = [NSMutableArray new];
   while ([marketResultSet next]) {
      OffreMarket *offerMarket = [OffreMarket new];
      ....
     [offers addObject:offerMarket];
   }

  market.offers = [offers copy];
}

return [offers copy]

}

这是有效的,但需要时间,因为我使用许多SQL请求来获取所有商品和相应的市场.

我可以避免许多SQL请求获取相应市场的所有优惠吗？谢谢你的回答

Answer 1

我可以建议的是:

• 优化您的SQL语句.您只需将语句更改为" SELECT * FROM OffreMarket WHERE codeOffer IN (SELECT code FROM Offer)" ,而不是2个循环.如果要name在表" Offer"中使用列" " ,则可以连接两个表" codeOffer"和" Offer".这里的经验法则是避免过多的循环,但尝试组合或优化您的SQL语句.

• code在表" Offer"中为列" " 创建索引.它会加速你的搜索速度.例如,在我的一个项目中,我不得不在具有36K记录的SQL表上工作.通过将简单索引设置为主键列,我设法将该表上的搜索时间缩短了10秒.