"Android" Greendao operation External DB database file

Last Update:2018-05-29 Source: Internet

Author: User

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1. backgroundThe so-called external database file here refers to a separately created in the external DB file, if there is a scenario, we have some local data in the project, do not need the interface to obtain (do not need to do network operations), write dead data, such as the provinces of the Country's various cities of the basic information, The information of each city can be stored as a record in the table, used in the project, how we have a db file containing this information, we can operate the db file through the greendao, more convenient for development work, of course, This is just a simulation situation, as for the unreasonable, There is no better way, but much discussion here, focusing on such a way, this way can be used for some infrequently changing Data.2. Project configuration <ul> <ul> <li>First look at the project Structure:</li> </ul> </ul>Res/raw directory is stored in the external DB file compressed file, we can open to look at the database structure, the DB file contains two tables, student and teacher inside the simple insert a few test data: <ul> <ul> <li>Introduce Greendao library files or reference library Projects:</li> </ul> </ul>2. Code ImplementationBefore the implementation of the specific idea, the program run, The Raw directory is the first copy of the DB file to the database storage default directory, and then through the Greendao API to operate the file; <ul> <ul> <ul> <li>We need to get the path to the application DB store, by the following way:</li> </ul> </ul> </ul><pre><pre>Private void Getappinfo () { // Get an instance of Packagemanager Packagemanager Packagemanager = Getpackagemanager (); // Getpackagename () is the package name of your current class, and 0 means to get version information Try { 0); } Catch (namenotfoundexception E) { e.printstacktrace (); } }</pre></pre> <ul> <ul> <ul> <li>The path to the database can be obtained in the above way: </li> <li>Copy operation:</li> </ul> </ul> </ul><pre> public StaticBoolean copyrawdbtoapkdb (context context,intcopyrawdbresid, string apkdbpath, string Dbname,boolean refresh) throws IOException {boolean b =false; File F=NewFile (apkdbpath); if(!f.exists ()) {f.mkdirs (); } File DBFile=NewFile (apkdbpath +dbName); b=isdbfileexists (dbfile,refresh); if(!B) {inputstream is=context.getresources (). Openrawresource (copyrawdbresid); Zipinputstream ZiS=NewZipinputstream (NewBufferedinputstream ( is)); ZipEntry entry; while((entry = Zis.getnextentry ())! =NULL) { intsize; byte[] buffer =New byte[1024x768*2]; OutputStream Fos=NewFileOutputStream (apkdbpath +Entry.getname ()); Bufferedoutputstream Bos=NewBufferedoutputstream (fos, buffer.length); while(size = Zis.read (buffer,0, buffer.length))! =-1) {bos.write (buffer,0, size); } Bos.flush (); Bos.close (); } zis.close (); is. Close (); } return!b; }</pre>Here is the copy operation of the key code, we need to pass in the raw resource id, the database copy path, database file name, whether to overwrite the existing DB file, @return copy is successful, about the refresh parameter, we generally want to copy only once, When we update the DB file in some cases, it can be set to True to overwrite the operation; <ul> <ul> <li>Using the Greendao Java project, generate the entity classes for the table corresponding to the external DB file DAO class Code:</li> </ul> </ul>In the Dbcontroller class is my encapsulated database operation class, more convenient for us to operate, Dbcontroller's key code is as Follows:<pre>/** * External database control class*/ public classdbcontroller{Private StaticDaomaster daomasterecmc; Private StaticDaomaster daomasterschool; //Default DB Private Staticdaosession daosessiondefault; //db of the copy Private Staticdaosession daoschoolsession; /** * Default database name: Localdata*/ public StaticFinal String database_name ="localdata.db"; /** * Copy Database Name: school*/ public StaticFinal String Database_school_name ="school.db"; Private Staticdaomaster obtainmaster (context context, String DbName) {return NewDaomaster (NewDaomaster.devopenhelper (context, dbName,NULL). getwritabledatabase ()); } Private Staticdaomaster getdaomaster (context context, String DbName) {if(dbName = =NULL) return NULL; if(DAOMASTERECMC = =NULL) {DAOMASTERECMC=Obtainmaster (context, dbName); } returndaomasterecmc; } Private Staticdaomaster getschooldaomaster (context context, String DbName) {if(dbName = =NULL) return NULL; if(daomasterschool = =NULL) {daomasterschool=Obtainmaster (context, dbName); } returndaomasterschool; } /** * Get daosession * * @return*/ public Staticdaosession getdaosession (String DbName) {if(daoschoolsession = =NULL) {daoschoolsession=getschooldaomaster (mainapplication.getins (), dbName). newsession (); } returndaoschoolsession; } /** * Default operation Localdata Database*/ public Staticdaosession getdaosession () {if(daosessiondefault = =NULL) {daosessiondefault=getdaomaster (mainapplication.getins (), database_name). newsession (); } returndaosessiondefault; }}</pre> <ul> <ul> <li>Perhaps we also need the default Greendao database for other operations, as the default operation is no longer described in detail here, do not understand the Greendao basic use, here we demonstrate the external db file named school.db, The default Greendao database is named history.db, and we test the operation in Mainactivity Below:</li> </ul> </ul><pre> public classMainactivity extends activity{PrivateStringBuilder builder; @Overrideprotected voidonCreate (Bundle Savedinstancestate) {super.oncreate (savedinstancestate); Setcontentview (r.layout.activity_main); //Create default data and insert a piece of dataHistorydao Historydao =dblocalcontroller.getdaosession (). Gethistorydao (); History entity=Newhistory (); Entity.setname ("Colorado"); Entity.setimageurl ("http://www.baidu.com"); Historydao.insert (entity); //copy the external db file to the specified directorycopyrawdb (); //querying external DB file data via GreendaoSeldbdata (); } Private voidseldbdata () {studentdao student=dbcontroller.getdaosession (dbcontroller.database_school_name). Getstudentdao (); List<Student> students =student.querybuilder (). List (); Builder=NewStringBuilder (); for(inti =0; I < students.size (); i++) {builder.append (students.Get(i). GetName () +"---"); } toast.maketext (mainactivity. this, builder.tostring (), toast.length_short). show (); } Private voidcopyrawdb () {Try { //copy Res/raw/xxxxdb.zip to//under The/data/data/com.xinhang.mobileclient/databases/directoryBoolean issuccess = Dbutils.copyrawdbtoapkdb (mainactivity. this, r.raw.schooldb, dbutils.apk_db_path, dbutils.ecmc_db_name,false); } Catch(ioexception E) {e.printstacktrace (); } }}</pre>Operation Result:You can see that our external db files have been copied to the default path of the database, and our default database has been created successfully, and the way to differentiate two databases is through the dblocalcontroller.getdaosession (name) method, To manipulate which database to pass in the corresponding database name, GIF operation diagram is as follows;

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