Column mapping with @Column in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the effect of @Column(name = "user_email") on a field?

Consider a Spring Boot entity with a field annotated as @Column(name = "user_email"). What does this annotation do?

Spring Boot

public class User {
  @Column(name = "user_email")
  private String email;
}

A Maps the field 'email' to the database column named 'user_email'.

B Renames the Java field 'email' to 'user_email' in the code.

C Creates a new database column 'email' and ignores 'user_email'.

D Automatically converts the field value to uppercase before saving.

💡 Hint

Think about how Java fields connect to database columns.

The @Column(name = "user_email") annotation tells Spring Boot to map the Java field email to the database column named user_email. It does not rename the Java field or change data values.

📝 Syntax

intermediate

Identify the correct @Column usage to set a column as non-nullable

Which option correctly uses @Column to make a database column NOT NULL?

Spring Boot

public class Product {
  @Column(??? )
  private String name;
}

A @Column(notNull = true)

B @Column(nullable = false)

C @Column(nullable = true)

D @Column(required = true)

💡 Hint

Check the exact attribute name for nullability in @Column.

The correct attribute to specify that a column cannot be null is nullable = false. Other options are invalid attributes.

🔧 Debug

advanced

Why does this @Column annotation cause a runtime error?

Given the entity field below, why will the application fail at runtime?

Spring Boot

public class Order {
  @Column(name = "order_date", length = 10)
  private LocalDate date;
}

A The 'length' attribute is invalid for LocalDate type causing a runtime error.

B The 'name' attribute must be omitted for LocalDate fields.

C The field 'date' must be public for @Column to work.

D LocalDate fields cannot be annotated with @Column.

💡 Hint

Consider which @Column attributes apply to which data types.

The 'length' attribute applies only to string-based columns. Using it on a LocalDate field causes a runtime error because the database column type does not support length.

❓ state_output

advanced

What is the database column name for this field?

Given the entity below, what is the exact database column name for the field userName?

Spring Boot

public class Account {
  @Column(name = "user_name")
  private String userName;
}

A USER_NAME

B username

C user_name

D userName

💡 Hint

Look at the name attribute inside @Column.

The name attribute explicitly sets the database column name to 'user_name'. The Java field name does not affect the column name when this attribute is present.

🧠 Conceptual

expert

What happens if @Column is omitted on a field?

In a Spring Boot JPA entity, if a field has no @Column annotation, what is the default behavior for database column mapping?

Spring Boot

public class Customer {
  private String address;
}

A The field is ignored and not mapped to any database column.

B The application throws an error because @Column is mandatory.

C The field is mapped to a column named 'column_address' automatically.

D The field is mapped to a column with the same name as the field, using default settings.

💡 Hint

Think about default JPA mapping conventions.

If @Column is omitted, JPA maps the field to a database column with the same name as the field, applying default column settings.