Formula (Hibernate Javadocs)

```
@Target({METHOD,FIELD})
@Retention(RUNTIME)
public @interface Formula
```
Specifies an expression written in native SQL that is used to read the value of an attribute instead of storing the value in a Column.
A Formula mapping defines a "derived" attribute, whose state is determined from other columns and functions when an entity is read from the database.
A formula may involve multiple columns and SQL operators:
```
 // perform calculations using SQL operators
 @Formula("sub_total * (1.0 + tax)")
 BigDecimal totalWithTax;
 
```
It may even call SQL functions:
```
 // call native SQL functions
 @Formula("upper(substring(middle_name from 0 for 1))")
 Character middleInitial;
 
```
For an entity with secondary tables, a formula may involve columns of the primary table, or columns of any one of the secondary tables. But it may not involve columns of more than one table.
The ColumnTransformer annotation is an alternative in certain cases, allowing the use of native SQL to read and write values to a column.
```
 // it might be better to use @ColumnTransformer in this case
 @Formula("decrypt(credit_card_num)")
 String getCreditCardNumber() { ... }
 
```
See Also:

ColumnTransformer, DiscriminatorFormula, JoinFormula, DialectOverride.Formula

- Required Element Summary
  
  Required Elements
  Modifier and Type Required Element Description
  
  String value
  The formula, written in native SQL.

- Element Detail
  - value
```
String value
```
    The formula, written in native SQL.