Preface ： Before using Android Built in database , It feels like a lot SQL sentence , If you're not careful, you're wrong , Very afflictive , I learned this LItePal Open source database framework , For a moment, I felt Android The built-in database is rubbish

LitePal GitHub home page ：https://github.com/LitePalFramework/LitePal

Configuration steps

1. Add dependency

Switch project Pattern , an APP Folder , find build.gradle file , Add dependencies to it , I'm using the latest version here , Can be in LitePal Of Github The latest version can be found on the official website

2. To configure LitePal.xml Files and related settings

stay main Create a new folder asstes Folder , after , establish LitePal.xml, Copy LitePal Upper GItHub The code given , Here I'll just write , among ,dbname Represents the name of the database ,version For version number ,list There's a table under the label （ The technical term is mapping model class ）, I'll talk about it later

Besides , We still need to AndroidMainfest Add a line of code to the file android:name="org.litepal.LitePalApplication"

3. Create a Java Bean class

Here's a book created bean class , There are three member variables , after , Use alt+insert, choice getter and setter, add to get And set Method

4. stay LItePal.xml In file list Tab （ Mapping model classes ）

Remember to write the package name completely

Use steps ：

1. Create and upgrade databases

In relation to activity Of java Direct use of documents LitePal Of getDatabase Method to create a database , Just add the following code , Written in onClick In the event , No screenshots here

LitePal.getDatabase();

Upgrade database , Directly in Bean Of java Add a new member variable and its get And set The method can , Upgrade the database code or use the above line of code

for instance , For example, the above , We want to add a publishing column , All we need to do is Book It creates a member variable , And get And set Method , after , Go to LitePal.xml In file , take version Version plus 1, That is to say, change it to 2 that will do , Nothing else needs to be changed

for example , We want to add another table , It's a similar operation , Create a Bean class , after , stay LitePal.xml Use... In the document mapping label , meanwhile , Add one to the version number , That is to say, change it to 2 that will do , Other things don't need to change

2. Add data

Modify model class （ That is to say Book）, To inherit DataSupport

after , We just need to create a new object , Call its set Method , Assign values to its member variables , after , call save Method , Is to successfully add data to the database

3. modify （ to update ） data

The operation of updating is very simple , Use udateAll The method can , for example , We're going to call it The Last The author of John, Change the price to 16

updateAll There are constraints in it , It's called The Last That piece of data , modify , If updateAll There are no parameters in it , That is to change the author and price of the data in the table to John and 16

4. Delete data

call DataSupport Of deleteAll Method , With the above updateAll similar , Parameters are filled with constraints , If you don't write , Delete the whole table 

 DataSupport.deleteAll(Book.class,"name is ?","The Last");// Delete name as The Last The data of 
 DataSupport.deleteAll(Book.class,"name is ? and price is ？","The Last","15");// Delete name as The Last, The price for 15 The data of 

DataSupport.deleteAll(Book.class,"price < ?","16");// Delete price below 16 The data of

5. Find data

Look for the DataSupport Of findAll The method can , Here is the sample code

select Specify the query column ,where Find the data that meets the constraints ,order Sort the query results ,limit Limit the number of query data 





 List<Book> books = DataSupport.findAll(Book.class);// lookup Book All the data in this table , Back to a List

List<Book> books1 = DataSupport.select("name","price").find(Book.class);// Specify query Book In this list name And price Two columns of data , It's also a List

List<Book> books2 = DataSupport.where("price > ?","16").find(Book.class);// Specified in the Book This table looks up prices that are greater than 16（ constraint condition ） The data of , Back to a List

List<Book> books4 = DataSupport.order("price desc").find(Book.class);// Sort the query results by price from high to low （desc Descending ）, Don't write or asc It's in ascending order 

List<Book> books5 = DataSupport.limit(3).find(Book.class);// Inquire about Book The first three data in the table 






  It is worth mentioning that , have access to findBySQL Method for Native Query , That's the way we used the built-in database before , Back to a Cursor object , I don't use it here 




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