Module is.codion.framework.domain
Package is.codion.framework.domain.entity.attribute

Interface Attribute<T>

Type Parameters:
T - the attribute type
All Known Subinterfaces:
Column<T>, ForeignKey
public sealed interface Attribute<T> permits Column<T>, ForeignKey (not exhaustive)
Typed Attribute representing a named, typed property of an entity.

Attributes are the building blocks of entity definitions, representing columns, foreign keys, derived values, or transient properties. Each attribute has a name, type, and is associated with a specific entity type.

Note that attribute names are case-sensitive and Attributes are equal if their names and entityTypes are equal, the attribute value type does not factor into equality.

Attributes are typically created through entity type factory methods and then configured using the as() method to create attribute definitions: 

interface InvoiceLine {
  EntityType TYPE = DOMAIN.entityType("chinook.invoiceline");

  // Typed columns, mapped to table columns
  Column<Long> ID = TYPE.longColumn("id");
  Column<BigDecimal> UNITPRICE = TYPE.bigDecimalColumn("unitprice");
  Column<Integer> QUANTITY = TYPE.integerColumn("quantity");

  // An attribute not mapped to a column, here a derived one
  Attribute<BigDecimal> TOTAL = TYPE.bigDecimalAttribute("total");
}

EntityDefinition invoiceLine() {
  return InvoiceLine.TYPE.as()
          .attributes(
                  InvoiceLine.ID.as()
                          .primaryKey(),
                  InvoiceLine.UNITPRICE.as()
                          .column()
                          .caption("Price")
                          .nullable(false),
                  InvoiceLine.QUANTITY.as()
                          .column()
                          .caption("Quantity")
                          .nullable(false)
                          .defaultValue(1),
                  InvoiceLine.TOTAL.as()
                          .derived()
                          .from(InvoiceLine.QUANTITY, InvoiceLine.UNITPRICE)
                          .with(new InvoiceLineTotal())
                          .caption("Total"))
          .build();
}

void attributes(Entities entities) {
  // Usage with entities
  Entity invoiceLine = entities.entity(InvoiceLine.TYPE)
          .with(InvoiceLine.UNITPRICE, BigDecimal.valueOf(0.99))
          .with(InvoiceLine.QUANTITY, 2)
          .build();

  // Type-safe value access
  BigDecimal unitPrice = invoiceLine.get(InvoiceLine.UNITPRICE);
  Integer quantity = invoiceLine.get(InvoiceLine.QUANTITY);
  BigDecimal total = invoiceLine.get(InvoiceLine.TOTAL); // 1.98

  // Attribute type information
  Class<BigDecimal> priceType = InvoiceLine.UNITPRICE.type().get(); // BigDecimal.class
  boolean numeric = InvoiceLine.QUANTITY.type().isNumeric();      // true
  boolean decimal = InvoiceLine.UNITPRICE.type().isDecimal();     // true
}
See Also: