diff --git a/app/src/androidTest/java/org/isoron/uhabits/unit/models/HabitTest.java b/app/src/androidTest/java/org/isoron/uhabits/unit/models/HabitTest.java
index d46826974..f31db5f35 100644
--- a/app/src/androidTest/java/org/isoron/uhabits/unit/models/HabitTest.java
+++ b/app/src/androidTest/java/org/isoron/uhabits/unit/models/HabitTest.java
@@ -19,6 +19,7 @@
 
 package org.isoron.uhabits.unit.models;
 
+import android.graphics.Color;
 import android.support.test.runner.AndroidJUnit4;
 import android.test.suitebuilder.annotation.SmallTest;
 
@@ -31,6 +32,8 @@ import java.util.LinkedList;
 import java.util.List;
 
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.nullValue;
+import static org.hamcrest.core.IsNot.not;
 import static org.junit.Assert.assertThat;
 
 @RunWith(AndroidJUnit4.class)
@@ -43,6 +46,49 @@ public class HabitTest
         HabitFixtures.purgeHabits();
     }
 
+    @Test
+    public void constructor_default()
+    {
+        Habit habit = new Habit();
+        assertThat(habit.archived, is(0));
+        assertThat(habit.highlight, is(0));
+
+        assertThat(habit.reminderDays, is(nullValue()));
+        assertThat(habit.reminderHour, is(nullValue()));
+        assertThat(habit.reminderMin, is(nullValue()));
+
+        assertThat(habit.streaks, is(not(nullValue())));
+        assertThat(habit.scores, is(not(nullValue())));
+        assertThat(habit.repetitions, is(not(nullValue())));
+        assertThat(habit.checkmarks, is(not(nullValue())));
+    }
+
+    @Test
+    public void constructor_habit()
+    {
+        Habit model = new Habit();
+        model.archived = 1;
+        model.highlight = 1;
+        model.color = Color.BLACK;
+        model.freqNum = 10;
+        model.freqDen = 20;
+        model.reminderDays = 1;
+        model.reminderHour = 8;
+        model.reminderMin = 30;
+        model.position = 0;
+
+        Habit habit = new Habit(model);
+        assertThat(habit.archived, is(model.archived));
+        assertThat(habit.highlight, is(model.highlight));
+        assertThat(habit.color, is(model.color));
+        assertThat(habit.freqNum, is(model.freqNum));
+        assertThat(habit.freqDen, is(model.freqDen));
+        assertThat(habit.reminderDays, is(model.reminderDays));
+        assertThat(habit.reminderHour, is(model.reminderHour));
+        assertThat(habit.reminderMin, is(model.reminderMin));
+        assertThat(habit.position, is(model.position));
+    }
+
     @Test
     public void reorderTest()
     {
diff --git a/app/src/main/java/org/isoron/helpers/DateHelper.java b/app/src/main/java/org/isoron/helpers/DateHelper.java
index 361b18cac..f89a3ef7b 100644
--- a/app/src/main/java/org/isoron/helpers/DateHelper.java
+++ b/app/src/main/java/org/isoron/helpers/DateHelper.java
@@ -32,6 +32,8 @@ import java.util.TimeZone;
 public class DateHelper
 {
     public static long millisecondsInOneDay = 24 * 60 * 60 * 1000;
+    public static int ALL_WEEK_DAYS = 127;
+
     private static Long fixedLocalTime = null;
 
     public static long getLocalTime()
diff --git a/app/src/main/java/org/isoron/helpers/DialogHelper.java b/app/src/main/java/org/isoron/helpers/DialogHelper.java
index ebaf6c9b5..c24083a7b 100644
--- a/app/src/main/java/org/isoron/helpers/DialogHelper.java
+++ b/app/src/main/java/org/isoron/helpers/DialogHelper.java
@@ -32,6 +32,7 @@ import android.view.View;
 import android.view.inputmethod.InputMethodManager;
 
 import org.isoron.uhabits.BuildConfig;
+import org.isoron.uhabits.commands.Command;
 
 public abstract class DialogHelper
 {
diff --git a/app/src/main/java/org/isoron/helpers/ReplayableActivity.java b/app/src/main/java/org/isoron/helpers/ReplayableActivity.java
index d2fcdc350..8f35b4bc7 100644
--- a/app/src/main/java/org/isoron/helpers/ReplayableActivity.java
+++ b/app/src/main/java/org/isoron/helpers/ReplayableActivity.java
@@ -26,6 +26,7 @@ import android.os.Bundle;
 import android.widget.Toast;
 
 import org.isoron.uhabits.R;
+import org.isoron.uhabits.commands.Command;
 
 import java.util.LinkedList;
 
diff --git a/app/src/main/java/org/isoron/uhabits/commands/ArchiveHabitsCommand.java b/app/src/main/java/org/isoron/uhabits/commands/ArchiveHabitsCommand.java
index 3aee23dc1..5e77c87d1 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/ArchiveHabitsCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/ArchiveHabitsCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
@@ -45,15 +44,13 @@ public class ArchiveHabitsCommand extends Command
     @Override
     public void execute()
     {
-        for(Habit h : habits)
-            h.archive();
+        Habit.archive(habits);
     }
 
     @Override
     public void undo()
     {
-        for(Habit h : habits)
-            h.unarchive();
+        Habit.unarchive(habits);
     }
 
     public Integer getExecuteStringId()
diff --git a/app/src/main/java/org/isoron/uhabits/commands/ChangeHabitColorCommand.java b/app/src/main/java/org/isoron/uhabits/commands/ChangeHabitColorCommand.java
index f9b00ba89..9abf7d5a7 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/ChangeHabitColorCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/ChangeHabitColorCommand.java
@@ -21,7 +21,6 @@ package org.isoron.uhabits.commands;
 
 import com.activeandroid.ActiveAndroid;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
@@ -47,22 +46,7 @@ public class ChangeHabitColorCommand extends Command
     @Override
     public void execute()
     {
-        ActiveAndroid.beginTransaction();
-
-        try
-        {
-            for(Habit h : habits)
-            {
-                h.color = newColor;
-                h.save();
-            }
-
-            ActiveAndroid.setTransactionSuccessful();
-        }
-        finally
-        {
-            ActiveAndroid.endTransaction();
-        }
+        Habit.setColor(habits, newColor);
     }
 
     @Override
diff --git a/app/src/main/java/org/isoron/helpers/Command.java b/app/src/main/java/org/isoron/uhabits/commands/Command.java
similarity index 96%
rename from app/src/main/java/org/isoron/helpers/Command.java
rename to app/src/main/java/org/isoron/uhabits/commands/Command.java
index 7472b096f..b9427e38a 100644
--- a/app/src/main/java/org/isoron/helpers/Command.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/Command.java
@@ -17,7 +17,7 @@
  * with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-package org.isoron.helpers;
+package org.isoron.uhabits.commands;
 
 public abstract class Command
 {
diff --git a/app/src/main/java/org/isoron/uhabits/commands/CommandFailedException.java b/app/src/main/java/org/isoron/uhabits/commands/CommandFailedException.java
new file mode 100644
index 000000000..b64722a88
--- /dev/null
+++ b/app/src/main/java/org/isoron/uhabits/commands/CommandFailedException.java
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2016 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.commands;
+
+public class CommandFailedException extends RuntimeException
+{
+    public CommandFailedException()
+    {
+        super();
+    }
+
+    public CommandFailedException(String message)
+    {
+        super(message);
+    }
+}
diff --git a/app/src/main/java/org/isoron/uhabits/commands/CreateHabitCommand.java b/app/src/main/java/org/isoron/uhabits/commands/CreateHabitCommand.java
index e3fba3e35..b3fe9499f 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/CreateHabitCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/CreateHabitCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
@@ -51,7 +50,10 @@ public class CreateHabitCommand extends Command
     @Override
     public void undo()
     {
-        Habit.get(savedId).delete();
+        Habit habit = Habit.get(savedId);
+        if(habit == null) throw new CommandFailedException("Habit not found");
+
+        habit.delete();
     }
 
     @Override
diff --git a/app/src/main/java/org/isoron/uhabits/commands/DeleteHabitsCommand.java b/app/src/main/java/org/isoron/uhabits/commands/DeleteHabitsCommand.java
index b1c2ee217..34e26c50c 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/DeleteHabitsCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/DeleteHabitsCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
diff --git a/app/src/main/java/org/isoron/uhabits/commands/EditHabitCommand.java b/app/src/main/java/org/isoron/uhabits/commands/EditHabitCommand.java
index ccd641c8b..aaca085d6 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/EditHabitCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/EditHabitCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
@@ -43,6 +42,8 @@ public class EditHabitCommand extends Command
     public void execute()
     {
         Habit habit = Habit.get(savedId);
+        if(habit == null) throw new CommandFailedException("Habit not found");
+
         habit.copyAttributes(modified);
         habit.save();
         if (hasIntervalChanged)
@@ -56,6 +57,8 @@ public class EditHabitCommand extends Command
     public void undo()
     {
         Habit habit = Habit.get(savedId);
+        if(habit == null) throw new CommandFailedException("Habit not found");
+
         habit.copyAttributes(original);
         habit.save();
         if (hasIntervalChanged)
diff --git a/app/src/main/java/org/isoron/uhabits/commands/ToggleRepetitionCommand.java b/app/src/main/java/org/isoron/uhabits/commands/ToggleRepetitionCommand.java
index fe573ddaf..451908433 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/ToggleRepetitionCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/ToggleRepetitionCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.models.Habit;
 
 public class ToggleRepetitionCommand extends Command
diff --git a/app/src/main/java/org/isoron/uhabits/commands/UnarchiveHabitsCommand.java b/app/src/main/java/org/isoron/uhabits/commands/UnarchiveHabitsCommand.java
index 08d34af69..79bd01d6e 100644
--- a/app/src/main/java/org/isoron/uhabits/commands/UnarchiveHabitsCommand.java
+++ b/app/src/main/java/org/isoron/uhabits/commands/UnarchiveHabitsCommand.java
@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.commands;
 
-import org.isoron.helpers.Command;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.models.Habit;
 
@@ -45,15 +44,13 @@ public class UnarchiveHabitsCommand extends Command
     @Override
     public void execute()
     {
-        for(Habit h : habits)
-            h.unarchive();
+        Habit.unarchive(habits);
     }
 
     @Override
     public void undo()
     {
-        for(Habit h : habits)
-            h.archive();
+        Habit.archive(habits);
     }
 
     public Integer getExecuteStringId()
diff --git a/app/src/main/java/org/isoron/uhabits/fragments/EditHabitFragment.java b/app/src/main/java/org/isoron/uhabits/fragments/EditHabitFragment.java
index a48087023..eddf1068e 100644
--- a/app/src/main/java/org/isoron/uhabits/fragments/EditHabitFragment.java
+++ b/app/src/main/java/org/isoron/uhabits/fragments/EditHabitFragment.java
@@ -39,16 +39,17 @@ import com.android.datetimepicker.time.RadialPickerLayout;
 import com.android.datetimepicker.time.TimePickerDialog;
 
 import org.isoron.helpers.ColorHelper;
-import org.isoron.helpers.Command;
 import org.isoron.helpers.DateHelper;
 import org.isoron.helpers.DialogHelper.OnSavedListener;
 import org.isoron.uhabits.R;
+import org.isoron.uhabits.commands.Command;
 import org.isoron.uhabits.commands.CreateHabitCommand;
 import org.isoron.uhabits.commands.EditHabitCommand;
 import org.isoron.uhabits.dialogs.WeekdayPickerDialog;
 import org.isoron.uhabits.models.Habit;
 
 import java.util.Arrays;
+import java.util.Date;
 
 public class EditHabitFragment extends DialogFragment
         implements OnClickListener, WeekdayPickerDialog.OnWeekdaysPickedListener,
@@ -136,7 +137,10 @@ public class EditHabitFragment extends DialogFragment
         }
         else if (mode == EDIT_MODE)
         {
-            originalHabit = Habit.get((Long) args.get("habitId"));
+            Long habitId = (Long) args.get("habitId");
+            if(habitId == null) throw new IllegalArgumentException("habitId must be specified");
+
+            originalHabit = Habit.get(habitId);
             modifiedHabit = new Habit(originalHabit);
 
             getDialog().setTitle(R.string.edit_habit);
@@ -178,14 +182,18 @@ public class EditHabitFragment extends DialogFragment
         editor.apply();
     }
 
+    @SuppressWarnings("ConstantConditions")
     private void updateReminder()
     {
-        if (modifiedHabit.reminderHour != null)
+        if (modifiedHabit.hasReminder())
         {
             tvReminderTime.setTextColor(Color.BLACK);
             tvReminderTime.setText(DateHelper.formatTime(getActivity(), modifiedHabit.reminderHour,
                     modifiedHabit.reminderMin));
             tvReminderDays.setVisibility(View.VISIBLE);
+
+            boolean weekdays[] = DateHelper.unpackWeekdayList(modifiedHabit.reminderDays);
+            tvReminderDays.setText(DateHelper.formatWeekdayList(getActivity(), weekdays));
         }
         else
         {
@@ -193,9 +201,6 @@ public class EditHabitFragment extends DialogFragment
             tvReminderTime.setText(R.string.reminder_off);
             tvReminderDays.setVisibility(View.GONE);
         }
-
-        boolean weekdays[] = DateHelper.unpackWeekdayList(modifiedHabit.reminderDays);
-        tvReminderDays.setText(DateHelper.formatWeekdayList(getActivity(), weekdays));
     }
 
     public void setOnSavedListener(OnSavedListener onSavedListener)
@@ -303,12 +308,13 @@ public class EditHabitFragment extends DialogFragment
         return valid;
     }
 
+    @SuppressWarnings("ConstantConditions")
     private void onDateSpinnerClick()
     {
         int defaultHour = 8;
         int defaultMin = 0;
 
-        if (modifiedHabit.reminderHour != null)
+        if (modifiedHabit.hasReminder())
         {
             defaultHour = modifiedHabit.reminderHour;
             defaultMin = modifiedHabit.reminderMin;
@@ -319,8 +325,11 @@ public class EditHabitFragment extends DialogFragment
         timePicker.show(getFragmentManager(), "timePicker");
     }
 
+    @SuppressWarnings("ConstantConditions")
     private void onWeekdayClick()
     {
+        if(!modifiedHabit.hasReminder()) return;
+
         WeekdayPickerDialog dialog = new WeekdayPickerDialog();
         dialog.setListener(this);
         dialog.setSelectedDays(DateHelper.unpackWeekdayList(modifiedHabit.reminderDays));
@@ -332,14 +341,14 @@ public class EditHabitFragment extends DialogFragment
     {
         modifiedHabit.reminderHour = hour;
         modifiedHabit.reminderMin = minute;
+        modifiedHabit.reminderDays = DateHelper.ALL_WEEK_DAYS;
         updateReminder();
     }
 
     @Override
     public void onTimeCleared(RadialPickerLayout view)
     {
-        modifiedHabit.reminderHour = null;
-        modifiedHabit.reminderMin = null;
+        modifiedHabit.clearReminder();
         updateReminder();
     }
 
@@ -357,12 +366,14 @@ public class EditHabitFragment extends DialogFragment
     }
 
     @Override
+    @SuppressWarnings("ConstantConditions")
     public void onSaveInstanceState(Bundle outState)
     {
         super.onSaveInstanceState(outState);
 
         outState.putInt("color", modifiedHabit.color);
-        if(modifiedHabit.reminderHour != null)
+
+        if(modifiedHabit.hasReminder())
         {
             outState.putInt("reminderMin", modifiedHabit.reminderMin);
             outState.putInt("reminderHour", modifiedHabit.reminderHour);
diff --git a/app/src/main/java/org/isoron/uhabits/fragments/ListHabitsFragment.java b/app/src/main/java/org/isoron/uhabits/fragments/ListHabitsFragment.java
index ef11a2301..51b24d696 100644
--- a/app/src/main/java/org/isoron/uhabits/fragments/ListHabitsFragment.java
+++ b/app/src/main/java/org/isoron/uhabits/fragments/ListHabitsFragment.java
@@ -46,7 +46,7 @@ import com.mobeta.android.dslv.DragSortController;
 import com.mobeta.android.dslv.DragSortListView;
 import com.mobeta.android.dslv.DragSortListView.DropListener;
 
-import org.isoron.helpers.Command;
+import org.isoron.uhabits.commands.Command;
 import org.isoron.helpers.DateHelper;
 import org.isoron.helpers.DialogHelper;
 import org.isoron.helpers.DialogHelper.OnSavedListener;
diff --git a/app/src/main/java/org/isoron/uhabits/fragments/ShowHabitFragment.java b/app/src/main/java/org/isoron/uhabits/fragments/ShowHabitFragment.java
index 1b7817afb..ba6c82d41 100644
--- a/app/src/main/java/org/isoron/uhabits/fragments/ShowHabitFragment.java
+++ b/app/src/main/java/org/isoron/uhabits/fragments/ShowHabitFragment.java
@@ -33,7 +33,7 @@ import android.widget.LinearLayout;
 import android.widget.TextView;
 
 import org.isoron.helpers.ColorHelper;
-import org.isoron.helpers.Command;
+import org.isoron.uhabits.commands.Command;
 import org.isoron.helpers.DialogHelper;
 import org.isoron.uhabits.HabitBroadcastReceiver;
 import org.isoron.uhabits.R;
diff --git a/app/src/main/java/org/isoron/uhabits/helpers/ReminderHelper.java b/app/src/main/java/org/isoron/uhabits/helpers/ReminderHelper.java
index 9a0e691d0..3f515396b 100644
--- a/app/src/main/java/org/isoron/uhabits/helpers/ReminderHelper.java
+++ b/app/src/main/java/org/isoron/uhabits/helpers/ReminderHelper.java
@@ -25,6 +25,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Build;
+import android.support.annotation.Nullable;
 import android.util.Log;
 
 import org.isoron.helpers.DateHelper;
@@ -43,13 +44,17 @@ public class ReminderHelper
             createReminderAlarm(context, habit, null);
     }
 
-    public static void createReminderAlarm(Context context, Habit habit, Long reminderTime)
+    public static void createReminderAlarm(Context context, Habit habit, @Nullable Long reminderTime)
     {
+        if(!habit.hasReminder()) return;
+
         if (reminderTime == null)
         {
             Calendar calendar = Calendar.getInstance();
             calendar.setTimeInMillis(System.currentTimeMillis());
+            //noinspection ConstantConditions
             calendar.set(Calendar.HOUR_OF_DAY, habit.reminderHour);
+            //noinspection ConstantConditions
             calendar.set(Calendar.MINUTE, habit.reminderMin);
             calendar.set(Calendar.SECOND, 0);
 
diff --git a/app/src/main/java/org/isoron/uhabits/models/Habit.java b/app/src/main/java/org/isoron/uhabits/models/Habit.java
index 02e3e67b6..851077189 100644
--- a/app/src/main/java/org/isoron/uhabits/models/Habit.java
+++ b/app/src/main/java/org/isoron/uhabits/models/Habit.java
@@ -21,6 +21,8 @@ package org.isoron.uhabits.models;
 
 import android.annotation.SuppressLint;
 import android.net.Uri;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.activeandroid.ActiveAndroid;
 import com.activeandroid.Model;
@@ -39,50 +41,113 @@ import java.util.List;
 @Table(name = "Habits")
 public class Habit extends Model
 {
+    /**
+     * Name of the habit
+     */
     @Column(name = "name")
     public String name;
 
+    /**
+     * Description of the habit
+     */
     @Column(name = "description")
     public String description;
 
+    /**
+     * Frequency numerator. If a habit is performed 3 times in 7 days, this field equals 3.
+     */
     @Column(name = "freq_num")
     public Integer freqNum;
 
+    /**
+     * Frequency denominator. If a habit is performed 3 times in 7 days, this field equals 7.
+     */
     @Column(name = "freq_den")
     public Integer freqDen;
 
+    /**
+     * Color of the habit. The format is the same as android.graphics.Color.
+     */
     @Column(name = "color")
     public Integer color;
 
+    /**
+     * Position of the habit. Habits are usually sorted by this field.
+     */
     @Column(name = "position")
     public Integer position;
 
+    /**
+     * Hour of the day the reminder should be shown. If there is no reminder, this equals to null.
+     */
+    @Nullable
     @Column(name = "reminder_hour")
     public Integer reminderHour;
 
+    /**
+     * Minute the reminder should be shown. If there is no reminder, this equals to null.
+     */
+    @Nullable
     @Column(name = "reminder_min")
     public Integer reminderMin;
 
+    /**
+     * Days of the week the reminder should be shown. This field can be converted to a list of
+     * booleans using the method DateHelper.unpackWeekdayList and converted back to an integer by
+     * using the method DateHelper.packWeekdayList. If there is no reminder, it equals null.
+     */
+    @Nullable
     @Column(name = "reminder_days")
     public Integer reminderDays;
 
+    /**
+     * Not currently used.
+     */
     @Column(name = "highlight")
     public Integer highlight;
 
+    /**
+     * Flag that indicates whether the habit is archived. Archived habits are usually omitted from
+     * listings, unless explicitly included.
+     */
     @Column(name = "archived")
     public Integer archived;
 
+    /**
+     * List of streaks belonging to this habit.
+     */
     public StreakList streaks;
+
+    /**
+     * List of scores belonging to this habit.
+     */
     public ScoreList scores;
+
+    /**
+     * List of repetitions belonging to this habit.
+     */
     public RepetitionList repetitions;
+
+    /**
+     * List of checkmarks belonging to this habit.
+     */
     public CheckmarkList checkmarks;
 
+    /**
+     * Constructs a habit with the same attributes as the specified habit.
+     *
+     * @param model the model whose attributes should be copied from
+     */
     public Habit(Habit model)
     {
         copyAttributes(model);
         initializeLists();
     }
 
+    /**
+     * Constructs a habit with default attributes. The habit is not archived, not highlighted, has
+     * no reminders and is placed in the last position of the list of habits.
+     */
     public Habit()
     {
         this.color = ColorHelper.palette[5];
@@ -91,7 +156,6 @@ public class Habit extends Model
         this.archived = 0;
         this.freqDen = 7;
         this.freqNum = 3;
-        this.reminderDays = 127;
         initializeLists();
     }
 
@@ -103,17 +167,36 @@ public class Habit extends Model
         checkmarks = new CheckmarkList(this);
     }
 
-    public static Habit get(Long id)
+    /**
+     * Returns the habit with specified id.
+     *
+     * @param id the id of the habit
+     * @return the habit, or null if none exist
+     */
+    @Nullable
+    public static Habit get(@NonNull Long id)
     {
         return Habit.load(Habit.class, id);
     }
 
+    /**
+     * Returns a list of all habits, optionally including archived habits.
+     *
+     * @param includeArchive whether archived habits should be included the list
+     * @return list of all habits
+     */
     public static List<Habit> getAll(boolean includeArchive)
     {
         if(includeArchive) return selectWithArchived().execute();
         else return select().execute();
     }
 
+    /**
+     * Changes the id of a habit on the database.
+     *
+     * @param oldId the original id
+     * @param newId the new id
+     */
     @SuppressLint("DefaultLocale")
     public static void updateId(long oldId, long newId)
     {
@@ -125,21 +208,32 @@ public class Habit extends Model
         return new Select().from(Habit.class).where("archived = 0").orderBy("position");
     }
 
-    public static From selectWithArchived()
+    protected static From selectWithArchived()
     {
         return new Select().from(Habit.class).orderBy("position");
     }
 
+    /**
+     * Returns the total number of unarchived habits.
+     *
+     * @return number of unarchived habits
+     */
     public static int count()
     {
         return select().count();
     }
 
+    /**
+     * Returns the total number of habits, including archived habits.
+     *
+     * @return number of habits, including archived
+     */
     public static int countWithArchived()
     {
         return selectWithArchived().count();
     }
 
+
     public static java.util.List<Habit> getHighlightedHabits()
     {
         return select().where("highlight = 1")
@@ -147,11 +241,22 @@ public class Habit extends Model
                 .execute();
     }
 
-    public static java.util.List<Habit> getHabitsWithReminder()
+    /**
+     * Returns a list the habits that have a reminder. Does not include archived habits.
+     *
+     * @return list of habits with reminder
+     */
+    public static List<Habit> getHabitsWithReminder()
     {
         return select().where("reminder_hour is not null").execute();
     }
 
+    /**
+     * Changes the position of a habit in the list.
+     *
+     * @param from the habit that should be moved
+     * @param to the habit that currently occupies the desired position
+     */
     public static void reorder(Habit from, Habit to)
     {
         if(from == to) return;
@@ -173,6 +278,10 @@ public class Habit extends Model
         from.save();
     }
 
+    /**
+     * Recompute the field position for every habit in the database. It should never be necessary
+     * to call this method.
+     */
     public static void rebuildOrder()
     {
         List<Habit> habits = selectWithArchived().execute();
@@ -196,6 +305,11 @@ public class Habit extends Model
 
     }
 
+    /**
+     * Copies all the attributes of the specified habit into this habit
+     *
+     * @param model the model whose attributes should be copied from
+     */
     public void copyAttributes(Habit model)
     {
         this.name = model.name;
@@ -211,12 +325,21 @@ public class Habit extends Model
         this.archived = model.archived;
     }
 
+    /**
+     * Saves the habit on the database, and assigns the specified id to it.
+     *
+     * @param id the id that the habit should receive
+     */
     public void save(Long id)
     {
         save();
         Habit.updateId(getId(), id);
     }
 
+    /**
+     * Deletes the habit and all data associated to it, including checkmarks, repetitions and
+     * scores.
+     */
     public void cascadeDelete()
     {
         Long id = getId();
@@ -238,25 +361,93 @@ public class Habit extends Model
         }
     }
 
+    /**
+     * Returns the public URI that identifies this habit
+     * @return the uri
+     */
     public Uri getUri()
     {
         return Uri.parse(String.format("content://org.isoron.uhabits/habit/%d", getId()));
     }
 
-    public void archive()
+    /**
+     * Returns whether the habit is archived or not.
+     * @return true if archived
+     */
+    public boolean isArchived()
     {
-        archived = 1;
-        save();
+        return archived != 0;
     }
 
-    public void unarchive()
+    private static void updateAttributes(List<Habit> habits, Integer color, Integer archived)
     {
-        archived = 0;
-        save();
+        ActiveAndroid.beginTransaction();
+
+        try
+        {
+            for (Habit h : habits)
+            {
+                if(color != null) h.color = color;
+                if(archived != null) h.archived = archived;
+                h.save();
+            }
+
+            ActiveAndroid.setTransactionSuccessful();
+        }
+        finally
+        {
+            ActiveAndroid.endTransaction();
+        }
     }
 
-    public boolean isArchived()
+    /**
+     * Archives an entire list of habits
+     *
+     * @param habits the habits to be archived
+     */
+    public static void archive(List<Habit> habits)
     {
-        return archived != 0;
+        updateAttributes(habits, null, 1);
+    }
+
+    /**
+     * Unarchives an entire list of habits
+     *
+     * @param habits the habits to be unarchived
+     */
+    public static void unarchive(List<Habit> habits)
+    {
+        updateAttributes(habits, null, 0);
+    }
+
+    /**
+     * Sets the color for an entire list of habits.
+     *
+     * @param habits the habits to be modified
+     * @param color the new color to be set
+     */
+    public static void setColor(List<Habit> habits, int color)
+    {
+        updateAttributes(habits, color, null);
+    }
+
+    /**
+     * Checks whether the habit has a reminder set.
+     *
+     * @return true if habit has reminder
+     */
+    public boolean hasReminder()
+    {
+        return (reminderHour != null && reminderMin != null && reminderDays != null);
+    }
+
+    /**
+     * Clears the reminder for a habit. This sets all the related fields to null.
+     */
+    public void clearReminder()
+    {
+        reminderHour = null;
+        reminderMin = null;
+        reminderDays = null;
     }
 }