Swift WCDB 联表查询教程：从数据库结构到结果获取

使用 WCDB 进行联表查询需要以下步骤：

定义数据库表结构：首先，需要定义每个表的结构，包括表名、字段名、字段类型等。可以使用 WCDB 提供的宏来定义表结构，例如：

#define TABLE_USER 'User'
#define TABLE_ADDRESS 'Address'

#define USER_COLUMN_ID 'id'
#define USER_COLUMN_NAME 'name'
#define USER_COLUMN_AGE 'age'

#define ADDRESS_COLUMN_ID 'id'
#define ADDRESS_COLUMN_USERID 'userId'
#define ADDRESS_COLUMN_ADDRESS 'address'

@interface User : NSObject <WCTTableCoding>

@property(nonatomic, assign) int64_t userId;
@property(nonatomic, copy) NSString *name;
@property(nonatomic, assign) int age;

WCDB_PROPERTY(userId)
WCDB_PROPERTY(name)
WCDB_PROPERTY(age)

@end

@interface Address : NSObject <WCTTableCoding>

@property(nonatomic, assign) int64_t addressId;
@property(nonatomic, assign) int64_t userId;
@property(nonatomic, copy) NSString *address;

WCDB_PROPERTY(addressId)
WCDB_PROPERTY(userId)
WCDB_PROPERTY(address)

@end

创建数据库并插入数据：使用 WCDB 提供的方法创建数据库，并插入测试数据。例如：

WCTDatabase *database = [WCTDatabase databaseWithFile:'path/to/database.sqlite'];
[database createTableWithName:TABLE_USER andClass:[User class]];
[database createTableWithName:TABLE_ADDRESS andClass:[Address class]];

User *user1 = [[User alloc] init];
user1.userId = 1;
user1.name = '张三';
user1.age = 20;
[database insertObject:user1 intoTable:TABLE_USER];

Address *address1 = [[Address alloc] init];
address1.addressId = 1;
address1.userId = 1;
address1.address = '北京市';
[database insertObject:address1 intoTable:TABLE_ADDRESS];

进行联表查询：使用 WCDB 提供的查询方法进行联表查询。例如，查询用户及其对应的地址：

WCTSelectBase *select = [[[[[[WCTSelectBase select:@[USER_COLUMN_NAME, ADDRESS_COLUMN_ADDRESS]]
    from:TABLE_USER]
    innerJoin:TABLE_ADDRESS]
    on:[WCTUser.class getPrimaryKeyName].column(USER_COLUMN_ID).equalTo(TABLE_ADDRESS.column(ADDRESS_COLUMN_USERID))]
    orderBy:USER_COLUMN_ID];
    
WCTStatement *statement = select.statement;
    
NSMutableArray *result = [NSMutableArray array];
    
[database executeStatements:statement
    withResultBlock:^int(NSDictionary *dictionary) {
        NSString *name = dictionary[USER_COLUMN_NAME];
        NSString *address = dictionary[ADDRESS_COLUMN_ADDRESS];
        [result addObject:@{@'name': name, @'address': address}];
        return 0;
    }];

以上就是使用 WCDB 进行联表查询的基本步骤。需要注意的是，WCDB 提供了丰富的查询语法和方法，可以根据具体需求进行灵活操作。