1.如果新加了一张数据表则什么都不用干直接database那里将数据库版本升1 就可以nichuang

在entities里增加新加的entity ProviderMeta.DB_VERSION 版本号增1

room会自动生成 一个ProviderMeta.DB_VERSION 版本号的json文件 比如实例中升级到70 就会生成一个70.json的文件这是room自动生成创建表的

2.原有数据表里增加了一个字段比如最后这行的devicetest

需要做的是 MIGRATION_68_69 写一个alertcolumn的sql exec

 

3.原有数据表如果是改变某个字段的名字 这时候需要复制老表的数据然后插入到新表 然后改变 databse版本号 

package com.voicevision.client.database.migrations

import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase
import com.voicevision.client.database.migrations.DatabaseMigrationUtil.KEYWORD_NOT_NULL
import com.voicevision.client.database.migrations.DatabaseMigrationUtil.TYPE_INTEGER
import com.voicevision.client.database.migrations.DatabaseMigrationUtil.TYPE_TEXT

/**
 * Migration from version 67 to 68.
 *
 * This migration makes the local_id column NOT NULL, with -1 as a default value.
 */
@Suppress("MagicNumber")
class Migration67to68 : Migration(67, 68) {
    override fun migrate(database: SupportSQLiteDatabase) {
        val tableName = "filelist"
        val newTableTempName = "${tableName}_new"
        val newColumns = mapOf(
            "_id" to DatabaseMigrationUtil.TYPE_INTEGER_PRIMARY_KEY,
            "filename" to TYPE_TEXT,
    、
        )

        DatabaseMigrationUtil.migrateTable(database, "filelist", newColumns) { columnName ->
            when (columnName) {
                "local_id" -> "IFNULL(local_id, -1)"
                else -> columnName
            }
        }
    }
}

package com.voicevision.client.database.migrations

import androidx.sqlite.db.SupportSQLiteDatabase

object DatabaseMigrationUtil {

    const val TYPE_TEXT = "TEXT"
    const val TYPE_INTEGER = "INTEGER"
    const val TYPE_INTEGER_PRIMARY_KEY = "INTEGER PRIMARY KEY"
    const val KEYWORD_NOT_NULL = "NOT NULL"

    /**
     * Utility method to add or remove columns from a table
     *
     * See individual functions for more details
     *
     * @param newColumns Map of column names and types on the NEW table
     * @param selectTransform a function that transforms the select statement. This can be used to change the values
     * when copying, such as for removing nulls
     */
    fun migrateTable(
        database: SupportSQLiteDatabase,
        tableName: String,
        newColumns: Map<String, String>,
        selectTransform: ((String) -> String)? = null
    ) {
        require(newColumns.isNotEmpty())
        val newTableTempName = "${tableName}_new"
        createNewTable(database, newTableTempName, newColumns)
        copyData(database, tableName, newTableTempName, newColumns.keys, selectTransform)
        replaceTable(database, tableName, newTableTempName)
    }

    /**
     * Utility method to create a new table with the given columns
     */
    private fun createNewTable(
        database: SupportSQLiteDatabase,
        newTableName: String,
        columns: Map<String, String>
    ) {
        val columnsString = columns.entries.joinToString(",") { "${it.key} ${it.value}" }
        database.execSQL("CREATE TABLE $newTableName ($columnsString)")
    }

    /**
     * Utility method to copy data from an old table to a new table. Only the columns in [columnNames] will be copied
     *
     * @param selectTransform a function that transforms the select statement. This can be used to change the values
     * when copying, such as for removing nulls
     */
    private fun copyData(
        database: SupportSQLiteDatabase,
        tableName: String,
        newTableName: String,
        columnNames: Iterable<String>,
        selectTransform: ((String) -> String)? = null
    ) {
        val selectColumnsString = columnNames.joinToString(",", transform = selectTransform)
        val destColumnsString = columnNames.joinToString(",")

        database.execSQL(
            "INSERT INTO $newTableName ($destColumnsString) " +
                "SELECT $selectColumnsString FROM $tableName"
        )
    }

    /**
     * Utility method to replace an old table with a new one, essentially deleting the old one and renaming the new one
     */
    private fun replaceTable(
        database: SupportSQLiteDatabase,
        tableName: String,
        newTableTempName: String
    ) {
        database.execSQL("DROP TABLE $tableName")
        database.execSQL("ALTER TABLE $newTableTempName RENAME TO $tableName")
    }
}