Entity relationship diagram

Official Mermaid documentation: Entity Relationship Diagram.

Note

All Mermaid diagrams can be configured, by passing a MermaidConfig object to any of the methods in the Mermaid class. Read more on Mermaid configuration.

Simple diagram

The following code sample shows how to create a simple entity relationship diagram.

Use the EntityRelationshipDiagram proerty of the Mermaid class to start building an entity relationship diagram.

Add entities to the diagram using the AddEntity method.

Add relationships between entities using the AddRelationship method.

Generate the diagram mermaid code with the Build method.

Example:

Mermaid
    .EntityRelationshipDiagram()
    .AddEntity("Customer", out var c)
    .AddEntity("Order", out var o)
    .AddEntity("Product", out var p)
    .AddRelationship(Cardinality.ExactlyOne, c, Cardinality.ZeroOrMore, o, "places")
    .AddRelationship(Cardinality.ExactlyOne, o, Cardinality.OneOrMore, p, "contains")
    .Build();

The code above generates the following Mermaid code:

erDiagram
    Customer ||--o{ Order : "places"
    Order ||--|{ Product : "contains"

That renders as:

erDiagram
    Customer ||--o{ Order : "places"
    Order ||--|{ Product : "contains"

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Cardinality

Cardinality must be defined for each end of a relationship and may be one of the following values:

• ZeroOrOne
• ExactlyOne
• ZeroOrMore
• OneOrMore

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Attributes

Attributes may be added to entities, using the optional attributes parameter of the AddEntity method.

Attributes must at least ave a type and a name. Thay can additionally have keys and a comment.

Example:

Mermaid
    .EntityRelationshipDiagram()
    .AddEntity("E1", out var e1, ("string", "foo"), ("int", "bar", EntityAttributeKeys.Primary | EntityAttributeKeys.Unique))
    .AddEntity("E2", out var e2, ("string", "baz", EntityAttributeKeys.Foreign, "hello"), ("int", "qux", "world"))
    .AddRelationship(Cardinality.ExactlyOne, e1, Cardinality.ZeroOrMore, e2, "has")
    .Build();

The code above generates the following Mermaid code:

erDiagram
    E1 {
        string foo
        int bar PK, UK
    }
    E2 {
        string baz FK "hello"
        int qux "world"
    }
    E1 ||--o{ E2 : "has"

That renders as:

erDiagram
    E1 {
        string foo
        int bar PK, UK
    }
    E2 {
        string baz FK "hello"
        int qux "world"
    }
    E1 ||--o{ E2 : "has"

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Identification

Relationships may be classified as either identifying (by default) or non-identifying and these are rendered with either solid or dashed lines respectively.

Use the optional relationshipType parameter of the AddRelationship method to specify the relationship type.

Example:

Mermaid
    .EntityRelationshipDiagram()
    .AddEntity("E1", out var e1)
    .AddEntity("E2", out var e2)
    .AddRelationship(Cardinality.ExactlyOne, e1, Cardinality.ZeroOrMore, e2, "foo", RelationshipType.NonIdentifying)
    .Build();

The code above generates the following Mermaid code:

erDiagram
    E1 ||..o{ E2 : "foo"

That renders as:

erDiagram
    E1 ||..o{ E2 : "foo"

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