Changing column types in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to change the column type of 'age' to integer in a Rails migration.

Ruby on Rails

change_column :users, :age, :[1]

Drag options to blanks, or click blank then click option'

Ainteger

Bboolean

Cstring

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Using :string instead of :integer

Forgetting the colon before the type

The change_column method changes the type of an existing column. Here, 'age' should be an integer.

2fill in blank

medium

Complete the migration code to change the 'price' column type to decimal.

Ruby on Rails

change_column :products, :price, :[1]

Drag options to blanks, or click blank then click option'

Ainteger

Bstring

Cdecimal

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using :float which can cause rounding errors

Using :string which is for text

Decimal type is used for precise numbers like prices.

3fill in blank

hard

Fix the error in this migration code to change 'published' column to boolean type.

Ruby on Rails

change_column :articles, :published, [1]

Drag options to blanks, or click blank then click option'

Abool

B:boolean

Cboolean

D:string

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the colon

Using 'bool' which is not a valid Rails type

The column type must be a symbol like :boolean in Rails migrations.

4fill in blank

hard

Fill both blanks to change the 'start_date' column to datetime and allow null values.

Ruby on Rails

change_column :events, :start_date, :[1], null: [2]

Drag options to blanks, or click blank then click option'

Adatetime

Btrue

Cfalse

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using :string instead of :datetime

Setting null: false when nulls are allowed

Use :datetime for date and time columns. Setting null: true allows null values.

5fill in blank

hard

Fill all three blanks to change 'score' column to float, set default to 0.0, and disallow nulls.

Ruby on Rails

change_column :games, :score, :[1], default: [2], null: [3]

Drag options to blanks, or click blank then click option'

Ainteger

B0.0

Cfalse

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using :integer for decimals

Setting null: true when nulls are not allowed

Float type stores decimal numbers. Default is set to 0.0 and null is disallowed with null: false.

Practice

1.

What is the primary Rails method used to change the type of an existing database column in a migration?

easy

A. change_column

B. rename_column

C. add_column

D. remove_column

Solution

1. Step 1: Understand migration methods

   Rails migrations provide specific methods for altering tables. add_column adds new columns, remove_column deletes columns, and rename_column changes column names.

2. Step 2: Identify method for changing column type

   The method change_column is designed to change the type of an existing column without removing it.

3. Final Answer:

   change_column -> Option A

4. Quick Check:

   Change column type = change_column [OK]

Hint: Use change_column to modify column types in migrations [OK]

Common Mistakes:

• Confusing change_column with rename_column
• Trying to use add_column to change type
• Using remove_column instead of changing type

2.

Which of the following is the correct syntax to change a column named price to type decimal with precision 8 and scale 2 in a Rails migration?

class ChangePriceTypeInProducts < ActiveRecord::Migration[7.0]
  def change
    ?
  end
end

easy

A. change_column :products, :price, :decimal, precision: 8, scale: 2

B. change_column :products, :price, :decimal(8,2)

C. change_column :products, :price, :decimal, {precision: 8, scale: 2}

D. change_column :products, :price, :decimal, precision => 8, scale => 2

Solution

1. Step 1: Review change_column syntax

   The correct syntax uses symbol keys for options: change_column(table, column, type, options). Options like precision and scale are passed as keyword arguments.

2. Step 2: Identify correct option format

   change_column :products, :price, :decimal, precision: 8, scale: 2 correctly uses precision: 8, scale: 2 as keyword arguments. change_column :products, :price, :decimal(8,2) uses invalid syntax. change_column :products, :price, :decimal, {precision: 8, scale: 2} uses a hash but without keyword arguments. change_column :products, :price, :decimal, precision => 8, scale => 2 uses hash rockets which is invalid in this context.

3. Final Answer:

   change_column :products, :price, :decimal, precision: 8, scale: 2 -> Option A

4. Quick Check:

   Keyword args for options = change_column :products, :price, :decimal, precision: 8, scale: 2 [OK]

Hint: Use keyword arguments for options in change_column [OK]

Common Mistakes:

• Using parentheses in type declaration like :decimal(8,2)
• Passing options as a hash without keywords
• Using old hash rocket syntax in options

3.

Given this migration snippet, what will be the new type of the age column after running it?

class ChangeAgeTypeInUsers < ActiveRecord::Migration[7.0]
  def change
    change_column :users, :age, :string
  end
end

medium

A. integer

B. boolean

C. string

D. float

Solution

1. Step 1: Read the change_column call

   The method call changes the age column in the users table to type :string.

2. Step 2: Understand the effect

   After running the migration, the age column will store string values instead of its previous type.

3. Final Answer:

   string -> Option C

4. Quick Check:

   change_column to :string = string [OK]

Hint: Look at the third argument of change_column for new type [OK]

Common Mistakes:

• Assuming the type stays the same
• Confusing column name with type
• Thinking change_column renames columns

4.

What is wrong with this migration code that tries to change a column type?

class ChangeActiveToBooleanInUsers < ActiveRecord::Migration[7.0]
  def change
    change_column :users, :active, 'boolean'
  end
end

medium

A. The column name should be a string, not a symbol

B. The type should be a symbol, not a string

C. change_column cannot change to boolean type

D. The migration class name is invalid

Solution

1. Step 1: Check argument types in change_column

   The method expects the type argument as a symbol, e.g., :boolean, not a string.

2. Step 2: Identify the error

   Using a string like 'boolean' will cause a syntax or runtime error because Rails expects symbols for types.

3. Final Answer:

   The type should be a symbol, not a string -> Option B

4. Quick Check:

   Type argument must be symbol = The type should be a symbol, not a string [OK]

Hint: Use symbols (e.g., :boolean) for types in change_column [OK]

Common Mistakes:

• Passing type as a string instead of symbol
• Thinking change_column can't handle boolean
• Misnaming migration class

5.

You want to change a column rating from integer to decimal with precision 3 and scale 1, but keep existing data safe. Which approach is best?

hard

A. Use change_column :table, :rating, :decimal, precision: 3, scale: 1 directly in one migration

B. Change the column type in the database manually without migration

C. Drop the column and add a new decimal column with the same name

D. Create a new decimal column, copy data with conversion, then remove old column and rename new one

Solution

1. Step 1: Understand risks of direct change_column

   Directly changing column type can cause data loss or errors if existing data doesn't fit new type.

2. Step 2: Use safe migration strategy

   Creating a new column, copying data with conversion, then removing old column and renaming new one ensures data safety and rollback ability.

3. Final Answer:

   Create a new decimal column, copy data with conversion, then remove old column and rename new one -> Option D

4. Quick Check:

   Safe type change = create-copy-rename [OK]

Hint: Avoid direct type change; copy data safely first [OK]

Common Mistakes:

• Directly changing type risking data loss
• Dropping column without backup
• Changing DB manually without migration