Basic use of iOS Databases

Basic use of iOS Databases

Summary of the basic usage of the database today:

The database used by iOS is generally sqlite3. before using the database, you must first import the database framework. Otherwise, an error occurs. Next, introduce the header file # import <sqlite3.h>

Create a Model class Student and a database tool class DataBaseTool in the project

Define several attributes in Student. h:

 

# Import <Foundation/Foundation. h>

 

@ Interface Student: NSObject

 

@ Property (nonatomic, copy) NSString * name;

 

@ Property (nonatomic, copy) NSString * holobby;

 

@ Property (nonatomic, assign) NSInteger age;

 

@ End

 

Database Operation Method declaration in DataBaseTool. h:

 

# Import <Foundation/Foundation. h>

 

# Import <sqlite3.h>

# Import "Student. h"

 

@ Interface DataBaseTool: NSObject

 

{

 

// Address used to save the database object

 

Sqlite3 * dbPoint;

 

}

 

// To ensure that the current database is unique in the project, we create a database tool object using a single instance.

 

+ (DataBaseTool *) define dataBaseTool;

 

// Open the database

 

-(Void) openDB;

 

// Create a table for the database.

 

-(Void) createTable;

 

// Insert a student information

 

-(Void) insertStu :( Student *) stu;

 

// Update the student information

 

-(Void) updateStu :( Student *) stu;

// Delete operation

 

-(Void) deletedateStu :( Student *) stu;

// Query operation

 

-(NSMutableArray *) selectAllStu;

 

// Close the database

 

-(Void) closeDB;

 

@ End

Implementation Method in DataBaseTool. m:

 

 

# Import "dataBaseTool. h"

 

@ Implementation dataBaseTool

 

+ (DataBaseTool *) specify dataBaseTool {

 

Static dataBaseTool * tool;

 

Static dispatch_once_t oneToken;

 

Dispatch_once (& oneToken, ^ {

 

Tool = [[dataBaseTool alloc] init];

 

});

 

Return tool;

 

}

 

-(Void) openDB {

 

// The database file is also saved in the hosts file of the sandbox, so first find the sandbox path

 

NSArray * sandBox = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES );

 

NSString * sandBoxPath = sandBox [0];

 

// Concatenate the file path. If the system finds the corresponding file based on the file path, it will open the database directly. If not, a corresponding database will be created.

 

NSString * documentPath = [sandBoxPath stringByAppendingPathComponent: @ "Student. sqlite"];

 

Int result = sqlite3_open ([documentPath UTF8String], & dbPoint );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "database opened successfully ");

 

NSLog (@ "% @", documentPath );

 

} Else {

NSLog (@ "database opening failed ");

}

}

 

-(Void) createTable {

 

// Primary key indicates the primary key. The primary key is unique in the current table and cannot be duplicated. It can uniquely identify a data record, usually an integer.

 

// Autoincrement auto-increment. In order to keep the primary key unique, the primary key will be auto-incrementing.

 

// If not exists is created only if no table exists, preventing duplicate creation and overwriting of previous data

 

// Database problem 90% is an SQL statement problem. Therefore, ensure that the statement is correct and then use it in the project.

 

NSString * sqlStr = @ "create table if not exists stu (number integer primary key autoincrement, name text, age integer, Hober text )";

 

// Execute this SQL statement

 

Int result = sqlite3_exec (dbPoint, [sqlStr UTF8String], nil );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "table created successfully ");

 

} Else {

NSLog (@ "Table creation failed ");

}

}

 

-(Void) insertStu :( Student *) stu {

 

NSString * sqlStr = [NSString stringWithFormat: @ "insert into stu (name, age, Hober) values ('% @', '% ld', '% @')", stu. name, stu. age, stu. holobby

 

];

 

// Execute the SQL statement

 

Int result = sqlite3_exec (dbPoint, [sqlStr UTF8String], nil );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "student added ");

 

} Else {

 

NSLog (@ "failed to add student ");

 

}

 

}

 

-(Void) updateStu :( Student *) stu {

 

NSString * sqlStr = [NSString stringWithFormat: @ "update stu set Hoby = '% @', age = % ld where name = '% @'", stu. holobby, stu. age, stu. name];

 

// Execute the SQL statement

 

Int result = sqlite3_exec (dbPoint, [sqlStr UTF8String], nil );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "updated successfully ");

 

} Else {

 

NSLog (@ "update failed ");

 

NSLog (@ "% d", result );

 

}

 

}

 

-(Void) deletedateStu :( Student *) stu {

 

NSString * sqlStr = [NSString stringWithFormat: @ "delete from stu where name = '% @'", stu. name];

 

// Execute the SQL statement

 

Int result = sqlite3_exec (dbPoint, [sqlStr UTF8String], nil );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "deleted successfully ");

 

} Else {

 

NSLog (@ "deletion failed ");

 

}

 

}

 

-(NSMutableArray *) selectAllStu {

 

// Query Logic

 

// 1. Read all data in a table from the local database first

 

// 2. Read the data one by one and assign values to the model.

 

// 3. Put the model that has been assigned a good value into the array and return

 

NSString * sqlStr = @ "select * from stu ";

 

// In the statement, * Indicates a wildcard. A * is used to replace all the field names in the table.

 

// Next we need to define a following pointer to traverse each row of data in the database table.

 

// The third parameter is the limit on the number of words in the query statement.-1 indicates no limit.

 

Sqlite3_stmt * stmt = nil;

 

Int result = sqlite3_prepare_v2 (dbPoint, [sqlStr UTF8String],-1, & stmt, nil );

 

// This method is equivalent to associating the database with the following pointer to complete the query function.

 

// Initialize an array for loading students

 

NSMutableArray * stuArr = [NSMutableArray array];

 

If (result = SQLITE_ OK ){

 

NSLog (@ "query successful ");

 

// Start traversing and querying each row of data in the database

 

While (sqlite3_step (stmt) = SQLITE_ROW ){

 

// Let the following pointer traverse the query. If there are no rows, the loop will be stopped.

 

// If the conditions are met, the content is read one by one

 

// The second parameter indicates the number of data columns in the current table.

 

Const unsigned char * name = sqlite3_column_text (stmt, 1 );

 

Int age = sqlite3_column_int (stmt, 2 );

 

Const unsigned char * holobby = sqlite3_column_text (stmt, 3 );

 

// Convert the data in the column type again

 

NSInteger stuAge = age;

 

NSString * stuName = [NSString stringwithuf8string :( const char *) name];

 

NSString * stuholobby = [NSString stringwithuf8string :( const char *) holobby];

 

// Assign a value to the object and put the object in the array

 

Student * stu = [[Student alloc] init];

 

Stu. name = stuName;

 

Stu. holobby = stuholobby;

 

Stu. age = stuAge;

 

[StuArr addObject: stu];

 

[Stu release];

 

}

 

} Else {

 

NSLog (@ "query failed ");

 

NSLog (@ "% d", result );

 

}

Return stuArr;

}

 

-(Void) closeDB {

 

Int result = sqlite3_close (dbPoint );

 

If (result = SQLITE_ OK ){

 

NSLog (@ "database closed successfully ");

 

// NSLog (@ "% @", documentPath );

} Else {

NSLog (@ "database shutdown failed ");

}

}

@ End