Android kotlin uses anko-sqlite database, CRUD

1. Using Anko SQLite in the project

Add anko-sqlitedependencies to your build.gradle（Module app）:

dependencies {
    implementation "org.jetbrains.anko:anko-sqlite:0.10.8"
}

2. Access the database

Anko provides a ManagedSQLiteOpenHelperspecial class that seamlessly replaces the default class. Here's how to use it:

class MyDatabaseOpenHelper private constructor(ctx: Context) : ManagedSQLiteOpenHelper(ctx, "MyDatabase", null, 1) {
    init {
        instance = this
    }

    companion object {
        private var instance: MyDatabaseOpenHelper? = null

        @Synchronized
        fun getInstance(ctx: Context) = instance ?: MyDatabaseOpenHelper(ctx.applicationContext)
    }

    override fun onCreate(db: SQLiteDatabase) {
        // 在这里创建表
        db.createTable("Customer", true, 
                    "id" to INTEGER + PRIMARY_KEY + UNIQUE,
                    "name" to TEXT,
                    "photo" to BLOB)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        // 在这里，您可以像往常一样升级表
        db.dropTable("User", true)
    }
}

// Context的访问属性
val Context.database: MyDatabaseOpenHelper
    get() = MyDatabaseOpenHelper.getInstance(this)

3. Create and delete tables

Using Anko, you can easily create new tables and delete existing tables. The syntax is very simple.

database.use {
    createTable("Customer", true, 
        "id" to INTEGER + PRIMARY_KEY + UNIQUE,
        "name" to TEXT,
        "photo" to BLOB)
}

In SQLite, there are five main types: NULL, INTEGER, REAL, TEXTand BLOB. But each column may have some modifiers like PRIMARY KEYor . UNIQUEYou can append such modifiers and "add" them to the main type name.

To delete a table, use the following dropTablefunction:

dropTable("User", true)

4. Insert data

// 其中db是SQLiteDatabase 
// 例如：val db = database.writeableDatabase 
db.insert("User", 
    "id" to 42,
    "name" to "John",
    "email" to "[email protected]"
)

Or database.use的internally:

database.use {
    insert("User", 
        "id" to 42,
        "name" to "John",
        "email" to "[email protected]"
   )
}

Note that in the above example databaseis a database helper instance and dbis an SQLiteDatabaseobject

The function insertOrThrow(), replace(), replaceOrThrow()also exists and has similar semantics.

5. Query data

Anko provides a convenient query builder. It can be created using an instance of  db.select(tableName, vararg columns)where  .dbSQLiteDatabase

method	describe
column(String)	Add a column to select query
distinct(Boolean)	Distinct query
whereArgs(String)	Specify raw String where query
whereArgs(String, args)	Specify a where query with arguments
whereSimple(String, args)	Specify a where query with ? mark arguments
orderBy(String, [ASC/DESC])	Order by this column
groupBy(String)	Group by this column
limit(count: Int)	Limit query result row count
limit(offset: Int, count: Int)	Limit query result row count with an offset
having(String)	Specify raw having expression
having(String, args)	Specify a having expression with arguments

 

Marked functions parse their arguments in a special way. They allow you to provide values ​​in any order and support seamless escaping.

db.select("User", "name")
    .whereArgs("(_id > {userId}) and (name = {userName})",
        "userName" to "John",
        "userId" to 42)