# Entity Relationship

Entities with attributes and the relationships between them.

## Examples

The playground samples for this type, rendered by Ondine when the documentation builds.

### Example 1

```mermaid
---
config:
  theme: default
  look: classic
  layout: dagre
---
erDiagram
  CUSTOMER ||--o{ ORDER : places
  ORDER ||--|{ LINE_ITEM : contains
  PRODUCT ||--o{ LINE_ITEM : "appears in"
  CUSTOMER {
    string name
    string email
  }
  ORDER {
    int id
    date placedAt
  }
  LINE_ITEM {
    int quantity
    float price
  }
  PRODUCT {
    string sku
    string title
  }

```

### Example 2

```mermaid
erDiagram
    CAR ||--o{ NAMED-DRIVER : allows
    CAR {
        string registrationNumber PK
        string make
        string model
        string[] parts
    }
    PERSON ||--o{ NAMED-DRIVER : is
    PERSON {
        string driversLicense PK "The license #"
        string(99) firstName "Only 99 characters are allowed"
        string lastName
        string phone UK
        int age
    }
    NAMED-DRIVER {
        string carRegistrationNumber PK, FK
        string driverLicense PK, FK
    }
    MANUFACTURER only one to zero or more CAR : makes

```

### Example 3

```mermaid
erDiagram
    direction TB
    CUSTOMER ||--o{ ORDER : places
    CUSTOMER {
        string name
        string custNumber
        string sector
    }
    ORDER ||--|{ LINE-ITEM : contains
    ORDER {
        int orderNumber
        string deliveryAddress
    }
    LINE-ITEM {
        string productCode
        int quantity
        float pricePerUnit
    }

```

### Example 4

```mermaid
erDiagram
    direction LR
    CUSTOMER ||--o{ ORDER : places
    CUSTOMER {
        string name
        string custNumber
        string sector
    }
    ORDER ||--|{ LINE-ITEM : contains
    ORDER {
        int orderNumber
        string deliveryAddress
    }
    LINE-ITEM {
        string productCode
        int quantity
        float pricePerUnit
    }

```

### Example 5

```mermaid
erDiagram
    subgraph title1
        CUSTOMER
        CUSTOMER {
            string name
            string custNumber
            string sector
        }
    end
    subgraph title2
        CAR ||--o{ NAMED-DRIVER : allows
        subgraph title3
            PERSON
            PERSON {
                string firstName
                string lastName
                int age
            }
        end
    end

```

### Example 6

```mermaid
erDiagram
    CAR {
        string registrationNumber
        string make
        string model
    }
    PERSON {
        string firstName
        string lastName
        int age
    }
    PERSON:::foo ||--|| CAR : owns
    PERSON o{--|| HOUSE:::bar : has

    classDef default fill:#f9f,stroke-width:4px
    classDef foo stroke:#f00
    classDef bar stroke:#0f0
    classDef foobar stroke:#00f

```