iOS database SQLite basic operations

<span id="Label3"></p><p><p>Several recommendations for database operations:</p></p> <ol> <ol> <li><p>Note the spelling of the string for the SQL execution Statement. (be sure to pay attention to spelling and suffer t_t)</p></li> <li><p>The usual functions of sqlite in OBJ-C.</p><p>(not a few,<strong>sqlite3_open</strong>, sqlite3_close,sqlite3_exec,sqlite3_perpare_v2,sqlite3_step,sqlite3_column_*, ...) ) (an additional two objects: Sqlite,sqlite_stmt)</p></li> <li><p>SQLite syntax. (common database operations are the Same)</p></li> <li><p>If you make a bigger project, the database operation is as encapsulated as Possible.</p></li> <li><p>Use your Search. (no less Detours)</p></li> </ol> </ol><p><p></p></p><p><p>Don't say much nonsense, the code adds comments:</p></p><p><p>Database path</p></p><p><p>Nsarray *paths = nssearchpathfordirectoriesindomains (nsdocumentdirectory, nsuserdomainmask, YES);</p></p><p><p>NSString *documentsdir = [paths objectatindex:0];</p></p><p><p>NSString *filepath = [documentsdir stringbyappendingpathcomponent:@ "test3.sqlite"];</p></p><p><p></p></p><p><p>Open Database</p></p><p><p>If (sqlite3_open ([filePath utf8string], &database)! = Sqlite_ok)</p></p><p><p>{</p></p><p><p>NSLog (@ "failed to open database");</p></p><p><p>}</p></p><p><p></p></p><p><p>Data execution operation encapsulation, do not want to encapsulate directly with sqlite3_exec function</p></p><p><p>Sqlite3_exec returns an enumeration value (shaping) that can perform operations such as creating tables, inserting, deleting, updating, etc.</p></p><p><p>-(int) execsql: (nsstring*) SQL</p></p><p><p>{</p></p><p><p>Char *errmsg;</p></p><p><p>If (sqlite3_exec (database, [sql utf8string], nil, nil, &errmsg)! = sqlite_ok) {</p></p><p><p>NSLog (@ "database Operation failed! ");</p></p><p><p>NSLog (@ "%s", errmsg);</p></p><p><p>Return sqlite_error;</p></p><p><p>}</p></p><p><p>Return sqlite_ok;</p></p><p><p>}</p></p><p><p></p></p><p><p>Call the encapsulated method to create the database</p></p><p><p>NSString *createtablehistory = @ "create table if not exists atable (id integer primary key autoincrement, acolumn nvarchar ( Not null); ";</p></p><p><p>[self execsql:createtablehistory];</p></p><p><p></p></p><p><p>Database query, (to be encapsulated)</p></p><p><p>Thing = [[nsmutablearray alloc] init];</p></p><p><p>NSString *selectsql = @ "select * from atable";</p></p><p><p>Sqlite3_stmt *statement;</p></p><p><p>If (sqlite3_prepare_v2 (database, [selectsql utf8string],-1, &statement, Nil) = = Sqlite_ok) {</p></p><p><p>While (sqlite3_step (statement) = = Sqlite_row) {</p></p><p><p>Nvarchar type query comes out is char*, assign value to nsstring words need to convert,</p></p><p><p>Note that this is the 1th column, and the number of columns starts from column No. 0.</p></p><p><p>If you want to query multiple fields, such as student information, you can package the student into a class and then put the case of that class into the array</p></p><p><p>[thing addobject:[nsstring stringwithutf8string: (char*) sqlite3_column_text (statement, 1)];</p></p><p><p>}</p></p><p><p>}</p></p><p><p>Else</p></p><p><p>{</p></p><p><p>NSLog (@ "data Query failed! ");</p></p><p><p>}</p></p><p><p></p></p><p><p>Last when the page closes, or the program closes remember to close the database</p></p><p><p>Sqlite3_close (database);</p></p><p><p>iOS database SQLite basic operations</p></p></span>