# Inheritance

## Introduction

Any database object can inherit from any other database object. The `Database` attribute is inherited from base- to subclasses. Hence, any class that directly or indirectly inherits a class with the `Database` attribute becomes a database class.

## Example

In this example, both `PrivateCustomer` and `CorporateCustomer` become database classes due to them inheriting `Customer`:

```csharp
[Database]
public class Customer
{
   public string Name { get; set; }
}

public class PrivateCustomer : Customer
{
   public string Gender { get; set; }
}

public class CorporateCustomer : Customer
{
   public string VatNumber { get; set; }
}
```

The table `Customer` will contain all `PrivateCustomers` and all `CorporateCustomers`. So if there is a private customer called "Goldman, Carl" and a corporate customer called "Goldman Sachs", the result of `SELECT C FROM Customer c` will contain both of them.

## Base Classes

A base class contains all instances of all derived classes in addition to the instances with the its own exact type.

```sql
SELECT C FROM Customer C WHERE Name LIKE 'Goldman%'
```

Returns `[ { Name:"Goldman Sachs" }, { Name:"Goldman, Carl" } ]`

## Derived classes

```sql
SELECT C FROM PrivateCustomer C WHERE Name LIKE 'Goldman%'
```

Returns `[{ Name:"Goldman, Carl", Gender:"Male" }]`

```sql
SELECT C FROM CorporateCustomer C WHERE Name LIKE 'Goldman%'
```

Returns `[{ Name:"Goldman Sachs", VatNumber:"1234" } ]`

## Inheriting From Non-Database Classes

A database class cannot inherit from a class that's not a database class. This will throw an error when the application is weaved.

It's also not possible to cast a non-database class to a database class.


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