FMDB （v2.5）一些需要知道的东西

1.SQLite，为个人应用程序和设备提供本地数据存储。SQLite，强调经济性，效率性，可靠性，独立性，和简单。SQLite的竞争对手fopen（）函数。

2.SQLite only supports one writer at a time per database file.But in most cases, a write transaction only takes milliseconds and so multiple writers
can simply take turns.SQLite will handle more write concurrency that many people suspect.Nevertheless,
client/server database systems, because they have a long-running server process at hand to coordinate access, can usually handle far more write concurrency than SQLite ever will.

官方文档中摘下来的，大概是说
sqlite 在工作的时候是锁库的。

3.用法：

 
  （1）三个主要的类

FMDatabase

 -代表一个单一的SQLite数据库。用于执行SQL语句。

   
   FMResultSet

 -代表了在执行查询的结果

FMDatabase。

      FMDatabaseQueue -如果你想在多个线程执行查询和更新，你会想使用这个类。

（2）创建

FMDatabase *db = [FMDatabase databaseWithPath:@"/tmp/tmp.db"];

if(![db  open]) { [db release];  return ; }

(3) 多条语句批次处理

NSString *sql = @"create table bulktest1 (id integer primary key autoincrement, x text);"
   
"create table bulktest2 (id integer primary key autoincrement, y text);"
   
"create table bulktest3 (id integer primary key autoincrement, z text);"
   
"insert into bulktest1 (x) values ('XXX');"
   
"insert into bulktest2 (y) values ('YYY');"
   
"insert into bulktest3 (z) values ('ZZZ');";

    
    success = [db executeStatements:sql];

    
    sql = @"select count(*) as count from bulktest1;"
   
"select count(*) as count from bulktest2;"
   
"select count(*) as count from bulktest3;";

    
    success = [self.db executeStatements:sql withResultBlock:^int(NSDictionary *dictionary) {
        NSInteger count = [dictionary[@"count"] integerValue];
        XCTAssertEqual(count, 1, @"expected one record for dictionary %@", dictionary);
        return 0;
    }];

（4）数据处理

INSERT INTO myTable的VALUES（？，？，？）

[db executeUpdate:@"INSERT INTO myTable VALUES (?)", @"this has \" lots of ' bizarre \" quotes '"];
  “？” 插入数值的占位符

另外，也可以使用命名参数语法：

INSERT INTO myTable的VALUES（：ID，：姓名，：值）
NSDictionary *argsDict = [NSDictionary dictionaryWithObjectsAndKeys:@"My Name", @"name", nil];

        [db executeUpdate:@"INSERT INTO myTable (name) VALUES (:name)" withParameterDictionary:argsDict];

提供给所有的参数-executeUpdate：方法（或任何接受该变种的va_list作为参数）必须是对象。下面将不起作用（并会导致崩溃）：

[db executeUpdate:@"INSERT INTO myTable VALUES (?)", 42];

正确的应该是：

[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:42]];
或者

[db executeUpdateWithFormat:@"INSERT INTO myTable VALUES (%d)", 42];

（5）在多线程中，使用FMDatabase的实例并不是明智的做法，这时候就应该想到FMDatabaseQueue了。

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:aPath];
   
[queue inDatabase:^(FMDatabase *db) {
       
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:1]];
       
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:2]];
       
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:3]];

        
       
FMResultSet *rs = [db executeQuery:@"select * from foo"];
       
while ([rs next]) {
            …
        }
   
}];

    
    [queue inTransaction:^(FMDatabase *db, BOOL *rollback) {
        [db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:1]];
        [db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:2]];
        [db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:3]];

        
        if (whoopsSomethingWrongHappened) {
            *rollback = YES;
            return;
        }
        // etc…
        [db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:4]];
    }];