Polymorphic

Update the account object to be polymorhpic structure that can support multiple types of accounts structures

• Savings
• Credit
• Retirement/Investment

Start by adding in support for a SavingsAccount and a CreditAccount classes to extend from Account

Make Account an abstract class

public abstract class Account {

Create an ENUM for the account type identifiers and add the property to the account class

public abstract AccountType getAccountType();

enum AccountType {
        SAVINGS,
        CHECKING,
        CREDIT,
        MONEY_MARKET,
        BUSINESS,
        INVESTMENT
    }

Implement the new instances that extend from Account using the example below

public class CreditAccount extends Account {
    
    public AccountType getAccountType() { return AccountType.SAVINGS; }
    
    // Additional methods as appropriate
}

Lastly add logic to the account class to allow Spring to know which type to instantiate in the controller level.

@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.PROPERTY,
        property = "accountType")
@JsonSubTypes({
        @JsonSubTypes.Type(value = CreditAccount.class, name = "CREDIT"),
        @JsonSubTypes.Type(value = SavingsAccount.class, name = "SAVINGS")
})
public abstract class Account {

Spring-Data will automatically add an attribute to each class specifying what concrete implementation is should be serialized back into.

{
  ...,
  _class: "com.mongodb.mongobank.models.SavingsAccount"
}

note

Adding additional properties to the individual class types will automatically ask MongoDB to persist them to the DB.

This enables you to be able to persist account types in the same collection. Some of the benefits include

• Ability query all accounts by customer without need for a union operation
• Ability to do aggregations and operations across all account types
• Simplified indexes and reduce index overhead

tip

MongoDB supports Partial indexes that can be applied only to object matching certain criteria. Use this to create indexes just for CreditAccount specific fields Allows reduced index size without need to break data into it's own collection.