SQL数据库的简单使用

一、 SQL数据库的建立，查询和删除等常用操作可以参考这个网址 http://www.w3school.com.cn/sql/
二、数据库的打开和关闭（iOS下要导入libsqlite3.dylib框架）

一般情况下会将其封装为一个单一的类，便于外界使用。

其 .h 中声明两个类方法，代码为

#import <Foundation/Foundation.h>
#import <sqlite3.h>
@interface DataBase : NSObject
// 打开数据库
+ (sqlite3 *)openDB;
// 关闭数据库
+ (void)closeDB;
@end

在 .m 中实现两个方法

#import "DataBase.h"
static sqlite3 *db;
@implementation DataBase
+ (sqlite3 *)openDB{
// 如果已经打开就直接返回数据库
if (db) {
return db;
}
// 获取document的路径
NSString *documentPath = [NSSearchPathForDirectoriesInDomains(9, 1, 1) lastObject];
// 拼接字符串
NSString *path = [documentPath stringByAppendingPathComponent:@"Students.sqlite"];
// 文件管理类对象（单例）
NSFileManager *fileManger = [NSFileManager defaultManager];
// 判断数据库是否在document中，不在的话将数据库文件拷贝至document，因为在应用包中的数据库文件是无法读取的，只有放在沙盒下才可以读取
if ([fileManger fileExistsAtPath:path] == NO) {
NSString *filePath = [[NSBundle mainBundle]pathForResource:@"Students" ofType:@"sqlite"];
[fileManger copyItemAtPath:filePath toPath:path error:nil];
}
sqlite3_open([path UTF8String], &db);
return db;

}
// 关闭数据库
+ (void)closeDB{
sqlite3_close(db);
}
@end

三、 一些具体的操作（取出所有数据， 删除， 更新，查找等）， 最好定义一个单例类，方便外界使用（因为其使用较为频繁）

1，需要定义一个类，比如Student，其内部代码

#import <Foundation/Foundation.h>

@interface Student : NSObject
@property(nonatomic, assign)int number;
@property(nonatomic, copy)NSString *name;
@property(nonatomic, copy)NSString *sex;
- (instancetype)initWithNumber:(int)number name:(NSString *)name sex:(NSString *)sex;
@end

#import "Student.h"

@implementation Student
- (instancetype)initWithNumber:(int)number name:(NSString *)name sex:(NSString *)sex{
self = [super init];
if (self) {
self.number = number;
self.name = name;
self.sex = sex;
}
return self;
}
@end

2，定义一个单例类，比如StudentHandle

现在.h 中声明几个方法

#import <Foundation/Foundation.h>
#import "Student.h"
@interface StudentHandle : NSObject
// 单例方法
+ (StudentHandle *)standardHandle;
// 取出所有对象
- (NSArray *)allStudents;
// 根据number取出某个对象
- (Student *)studentByNumber:(int)number;
// 插入数据
- (BOOL)insertStudentWithName:(NSString *)name sex:(NSString *)sex;
// 删除数据
- (BOOL)deleteStudentByNumber:(int)number;
// 更新数据
- (BOOL)updateStudentWithName:(NSString *)name byNumber:(int)number;
@end

#import "StudentHandle.h"
#import "DataBase.h"
@implementation StudentHandle
// 创建单例
static StudentHandle *studentHandle = nil;
+ (StudentHandle *)standardHandle{
@synchronized(self){
if (studentHandle == nil) {
studentHandle = [[StudentHandle alloc] init];
}
return studentHandle;
}
}

- (NSArray *)allStudents{
// 1，打开数据库
sqlite3 *db = [DataBase openDB];
// 2，准备SQL语句
sqlite3_stmt *stmt = nil;
int result = sqlite3_prepare(db, "select * from StudentInfo", -1, &stmt, nil);
NSMutableArray *arr = nil;
if (result == SQLITE_OK) {
// 3,执行stmt
arr = [NSMutableArray arrayWithCapacity:0];
while (sqlite3_step(stmt) == SQLITE_ROW) {
// 4，获取数据
int number = sqlite3_column_int(stmt, 0);
const unsigned char *nameUTF = sqlite3_column_text(stmt, 1);
const unsigned char *sexUTF = sqlite3_column_text(stmt, 2);
Student *stu = [[Student alloc] initWithNumber:number name:[NSString stringWithUTF8String:(const char *)nameUTF] sex:[NSString stringWithUTF8String:(const char *)sexUTF]];
[arr addObject:stu];
}

}
// 释放stmt所占用的内存
sqlite3_finalize(stmt);
return arr;

}
- (Student *)studentByNumber:(int)number{
sqlite3 *db = [DataBase openDB];
sqlite3_stmt *stmt = nil;
int result = sqlite3_prepare_v2(db, "select name,number, sex from StudentInfo where number = ?", -1, &stmt, nil);
Student *stu = nil;
if (result == SQLITE_OK) {
sqlite3_bind_int(stmt, 1, number);
if (sqlite3_step(stmt) == SQLITE_ROW) {
const unsigned char *nameUTF = sqlite3_column_text(stmt, 0);
int number = sqlite3_column_int(stmt, 1);
const unsigned char *sexUTF = sqlite3_column_text(stmt, 2);
stu = [[Student alloc] initWithNumber:number name:[NSString stringWithUTF8String:(const char *)nameUTF] sex:[NSString stringWithUTF8String:(const char *)sexUTF]];
}

}
sqlite3_finalize(stmt);
return stu;
}

- (BOOL)insertStudentWithName:(NSString *)name sex:(NSString *)sex{
sqlite3 *db = [DataBase openDB];
sqlite3_stmt *stmt = nil;
int result = sqlite3_prepare_v2(db, "insert into StudentInfo (name, sex) values (?, ?)", -1, &stmt, nil);
BOOL insertInfo = NO;
if (result == SQLITE_OK) {
sqlite3_bind_text(stmt, 1, [name UTF8String], -1, nil);
sqlite3_bind_text(stmt, 2, [sex UTF8String], -1, nil);
if (sqlite3_step(stmt) == SQLITE_DONE) {
insertInfo = YES;
}
}
sqlite3_finalize(stmt);
return insertInfo;
}

- (BOOL)deleteStudentByNumber:(int)number{
sqlite3 *db = [DataBase openDB];
sqlite3_stmt *stmt = nil;
int result = sqlite3_prepare_v2(db, "delete from StudentInfo where number = ?", -1, &stmt, nil);
BOOL deleteInfo = NO;

if (result == SQLITE_OK) {
sqlite3_bind_int(stmt, 1, number);
if (sqlite3_step(stmt) == SQLITE_DONE) {
deleteInfo = YES;
}
}
sqlite3_finalize(stmt);
return deleteInfo;
}
- (BOOL)updateStudentWithName:(NSString *)name byNumber:(int)number{
sqlite3 *db = [DataBase openDB];
sqlite3_stmt *stmt = nil;
int result = sqlite3_prepare_v2(db, "update StudentInfo set name = ? where number = ?", -1, &stmt, nil);
BOOL updateInfo = NO;
if (result == SQLITE_OK) {

sqlite3_bind_text(stmt, 1, [name UTF8String], -1, nil);
sqlite3_bind_int(stmt, 2, number);

if (sqlite3_step(stmt) == SQLITE_DONE) {
return updateInfo = YES;
}

}
sqlite3_finalize(stmt);
return updateInfo;
}
@end