iOS Development Database Chapter-fmdb Brief Introduction

iOS Development Database Chapter-fmdb Brief Introduction

A simple explanation

1. What is Fmdb

Fmdb is the SQLite database framework for the iOS platform

Fmdb encapsulates the C language API of SQLite in OC mode

Advantages of 2.FMDB

Use more object-oriented, save a lot of cumbersome, redundant C language code

More lightweight and flexible compared to Apple's own core data framework

Provides a multi-threaded secure database operation method to effectively prevent data confusion

GitHub address for 3.FMDB

Https://github.com/ccgus/fmdb

Second, the Core class

Fmdb has three main classes

(1) Fmdatabase

A Fmdatabase object represents a single SQLite database

Used to execute SQL statements

(2) Fmresultset

Result set after query execution with Fmdatabase

(3) Fmdatabasequeue

Used to execute multiple queries or updates in multiple threads, which is thread-safe

Third, open the database

To create a Fmdatabase object by specifying the SQLite database file path

Fmdatabase *db = [Fmdatabase Databasewithpath:path];

if (![ DB Open]) {

NSLog (@ "Database open failed! ");

}

There are three types of file paths

(1) Specific file path

Automatically created if it does not exist

(2) empty string @ ""

An empty database is created in the temp directory

The database file is also deleted when the Fmdatabase connection is closed

(3) Nil

An in-memory staging database is created and the database is destroyed when the Fmdatabase connection is closed

Iv. implementation of the update

In Fmdb, all operations except queries are called "updates"

Create, DROP, insert, UPDATE, delete, and more

To perform an update using the Executeupdate: method

-(BOOL) Executeupdate: (nsstring*) SQL, ...

-(BOOL) Executeupdatewithformat: (nsstring*) format, ...

-(BOOL) Executeupdate: (nsstring*) SQL Withargumentsinarray: (Nsarray *) arguments

Example

[DB executeupdate:@ "UPDATE t_student SET age =? WHERE name =?; ", @20, @" Jack "]

V. Execution of inquiries

Query method

-(Fmresultset *) ExecuteQuery: (nsstring*) SQL, ...

-(Fmresultset *) Executequerywithformat: (nsstring*) format, ...

-(Fmresultset *) ExecuteQuery: (NSString *) SQL Withargumentsinarray: (Nsarray *) arguments

Example

Querying data

Fmresultset *rs = [db executequery:@ "select * from T_student"];

Traversing result Sets

while ([Rs next]) {

NSString *name = [rs stringforcolumn:@ "name"];

int age = [rs intforcolumn:@ ' age '];

Double score = [Rs doubleforcolumn:@ "score"];

}

Vi. code Examples

1. Create a new project, import the Libsqlite3 library, and include the primary header file in the project

2. Download the third-party framework Fmdb

　　

3. Sample Code

YYVIEWCONTROLLER.M file

1 //2 //YYVIEWCONTROLLER.M3 //04-fmdb Basic Use4 //5 //Created by Apple on 14-7-27.6 //Copyright (c) 2014 wendingding. All rights reserved.7 //8 9 #import "YYViewController.h"Ten #import "FMDB.h" One  A @interfaceYyviewcontroller () -@property (nonatomic,strong) fmdatabase *db; - @end the  - @implementationYyviewcontroller -  -- (void) Viewdidload + { - [Super Viewdidload]; +     //1. Get the path to the database file ANSString *doc=[Nssearchpathfordirectoriesindomains (NSDocumentDirectory, Nsuserdomainmask, YES) lastobject]; atNSString *filename=[doc stringbyappendingpathcomponent:@"Student.sqlite"]; -      -     //2. Access to the database -Fmdatabase *db=[Fmdatabase databasewithpath:filename]; -      -     //3. Open the Database in     if([db Open]) { -         //4. Create a watch toBOOL result=[db executeupdate:@"CREATE TABLE IF not EXISTS t_student (ID integer PRIMARY KEY autoincrement, name text NOT NULL, age integer NOT NULL); "]; +         if(Result) { -NSLog (@"success in the creation of a table"); the}Else *         { $NSLog (@"failed to create a table");Panax Notoginseng         } -     } theself.db=db; +  A } the  +-(void) Touchesbegan: (Nsset *) touches withevent: (Uievent *)Event - { $ [self delete]; $ [self insert]; - [self query]; - } the  - //Inserting DataWuyi-(void) Insert the { -      for(inti =0; i<Ten; i++) { WuNSString *name = [NSString stringWithFormat:@"jack-%d", Arc4random_uniform ( -)]; -         //executeupdate: Indeterminate parameters are used to occupy the position About[Self.db executeupdate:@"INSERT into T_student (name, age) VALUES (?,?);", Name, @ (Arc4random_uniform ( +))]; $         //[self.db executeupdate:@ "INSERT into T_student (name, age) VALUES (?,?);" Withargumentsinarray:@[name, @ (ARC4 Random_uniform (+))]; -          -         //Executeupdatewithformat: Indeterminate parameters are occupied by%@,%d, etc. -         //[self.db executeupdatewithformat:@ "INSERT into T_student (name, age) VALUES (%@,%d);", Name, Arc4random_unifo RM (+)]; A     } + } the  - //Delete Data $-(void) Delete the { the     //[self.db executeupdate:@ "DELETE from T_student;"]; the[Self.db executeupdate:@"DROP TABLE IF EXISTS t_student;"]; the[Self.db executeupdate:@"CREATE TABLE IF not EXISTS t_student (ID integer PRIMARY KEY autoincrement, name text NOT NULL, age integer NOT NULL); "]; - } in  the //Enquiry the- (void) Query About { the     //1. Execute the query statement theFmresultset *resultset = [self.db executeQuery:@"SELECT * from T_student"]; the      +     //2. Traverse the results -      while([ResultSet next]) { the         intID = [ResultSet intforcolumn:@"ID"];BayiNSString *name = [ResultSet stringforcolumn:@"name"]; the         intAge = [ResultSet intforcolumn:@" Age"]; theNSLog (@"%d%@%d", ID, name, age); -     } - } the  the @end

Print View results:

Tips:

If the ID is set to gradual and is set to autogrow, then after deleting the data in the table, reinsert the new data, the ID number is not starting from 0, but the previous ID is numbered.

Attention:

Do not write the following form, do not add ', directly using%@, it will automatically think that this is a string.