aamg

ActiveAndroid migration generator

This is a small tool that analyzes your code, and generates a migration script for your models.

Example

Let's say that you have two models in your code:

$ cat Item.java
@Table(name = "Items")
public class Item extends Model {
    @Column
    public String name;

    @Column
    public Category category;

    @Column
    public Double price;
}

$ cat Category.java
@Table
public class Category extends Model {
    @Column
    public String name;

    public List<Item> items() {
        return getMany(Item.class, "Category");
    }
}

OK, now let's see what was added during the last commit:

$ git log --pretty=oneline
69889d65092d159bf2b2d6d7bc9f91ad33eb058b added price to item
cb3188e95149f9f78cc763906e4ce91fe4ba9818 first version

$ git show 69889d65092d159bf2b2d6d7bc9f91ad33eb058b
commit 69889d65092d159bf2b2d6d7bc9f91ad33eb058b
Author: Benoit Duffez <benoit.duffez@upactivity.com>
Date:   Tue Apr 11 14:26:37 2017 +0200

    added price to item

diff --git a/Item.java b/Item.java
index a9f497e..97534b5 100644
--- a/Item.java
+++ b/Item.java
@@ -5,5 +5,8 @@ public class Item extends Model {

         @Column
         public Category category;
+
+        @Column
+        public Double price;
 }

The price was added to Item. What would be the migration script?

$ java -cp ~/projects/aamg/ GenerateAaMigration Item.java 69889d65092d159bf2b2d6d7bc9f91ad33eb058b
BEGIN TRANSACTION;

ALTER TABLE items ADD COLUMN price REAL;

COMMIT;

Drop columns

The tool can be launched without the SHA1 argument, in which case it will compare the current state of the files with HEAD:

$ git diff
diff --git a/Category.java b/Category.java
index 94ca9fd..e04e7eb 100644
--- a/Category.java
+++ b/Category.java
@@ -1,7 +1,10 @@
 @Table
 public class Category extends Model {
     @Column
-    public String name;
+    public int color;
+
+    @Column
+    public String description;

     public List<Item> items() {
         return getMany(Item.class, "Category");

Here the name column was dropped, and two other columns are created:

$ java -cp ~/projects/aamg/ GenerateAaMigration Category.java
BEGIN TRANSACTION;

CREATE TABLE category_backup (Id INTEGER PRIMARY KEY AUTOINCREMENT, color INTEGER, description TEXT);
INSERT INTO category_backup (Id) SELECT Id FROM category;
DROP TABLE category;
ALTER TABLE category_backup RENAME TO category;

COMMIT;

Since we can't drop columns with SQLite, a copy of the table is made and the data is inserted in the new table.

What about TypeSerializers

OK now let's assume that we don't want to use an int in the code for the color, but an object. Let's see how it looks like:

$ cat Color.java
class Color {
    public int red, green, blue;
    Color(int r, int g, int b) {
        red = r;
        green = g;
        blue = b;
    }
}

$ cat ColorSerializer.java
import com.activeandroid.serializer.TypeSerializer;

public class ColorSerializer extends TypeSerializer {
    @Override
    public Class<?> getDeserializedType() {
        return Color.class;
    }

    @Override
    public Class<?> getSerializedType() {
        return Integer.class;
    }

    @Override
    public Integer serialize(Object data) {
        if (data == null || !(data instanceof Color)) {
            return null;
        }
        Color color = (Color) data;
        return color.red << 16 + color.green << 8 + color.blue;
    }

    @Override
    public Form deserialize(Object data) {
        if (data == null || !(data instanceof Integer)) {
            return null;
        }
        Integer color = (Integer) data;
        return new Color((color >> 16) & 0xff, (color >> 8) & 0xff, color & 0xff);
    }
}

The TypeSerializer simply stores the Color object in the DB by packing/unpacking an integer.

Now let's see our model:

$ git diff Category.java
diff --git a/Category.java b/Category.java
index e04e7eb..c2aeddd 100644
--- a/Category.java
+++ b/Category.java
@@ -1,7 +1,7 @@
 @Table
 public class Category extends Model {
     @Column
-    public int color;
+    public Color rgb;

     @Column
     public String description;

Since we can't change a column type, we renamed it. See the result:

$ java -cp ~/projects/aamg/ GenerateAaMigration Category.java
BEGIN TRANSACTION;

CREATE TABLE category_backup (Id INTEGER PRIMARY KEY AUTOINCREMENT, rgb INTEGER, description TEXT);
INSERT INTO category_backup (Id, description) SELECT Id, description FROM category;
DROP TABLE category;
ALTER TABLE category_backup RENAME TO category;

COMMIT;

The tool correctly understood that the rgb column is stored as an INTEGER in the database.