chore: update ER diagram docs

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

.changeset/angry-trains-fall.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix: Make relationship-label optional in ER diagrams

cypress/integration/rendering/erDiagram.spec.js

@@ -322,6 +322,18 @@ ORDER ||--|{ LINE-ITEM : contains
     );
   });
 
+  it('should render an ER diagram  without labels also', () => {
+    imgSnapshotTest(
+      `
+    erDiagram
+        BOOK }|..|{ AUTHOR 
+        BOOK }|..|{ GENRE
+        AUTHOR }|..|{ GENRE 
+      `,
+      { logLevel: 1 }
+    );
+  });
+
   it('should render relationship labels with line breaks', () => {
     imgSnapshotTest(
       `

docs/syntax/entityRelationshipDiagram.md

@@ -135,6 +135,44 @@ erDiagram
     "This **is** _Markdown_"
 ```
 
+#### Optional Relationship Labels
+
+Starting from Mermaid version 11.11.0, the relationship label in ER diagrams is optional. You can define relationships without specifying a label, and the diagram will render correctly.
+
+For example, the following is valid:
+
+```mermaid-example
+erDiagram
+    BOOK }|..|{ AUTHOR
+    BOOK }|..|{ GENRE
+    AUTHOR }|..|{ GENRE
+```
+
+```mermaid
+erDiagram
+    BOOK }|..|{ AUTHOR
+    BOOK }|..|{ GENRE
+    AUTHOR }|..|{ GENRE
+```
+
+This will show the relationships between the entities without any labels on the connecting lines.
+
+You can still add a label if you want to describe the relationship:
+
+```mermaid-example
+erDiagram
+    BOOK }|..|{ AUTHOR : written_by
+    BOOK }|..|{ GENRE : categorized_as
+    AUTHOR }|..|{ GENRE : specializes_in
+```
+
+```mermaid
+erDiagram
+    BOOK }|..|{ AUTHOR : written_by
+    BOOK }|..|{ GENRE : categorized_as
+    AUTHOR }|..|{ GENRE : specializes_in
+```
+
 ### Relationship Syntax
 
 The `relationship` part of each statement can be broken down into three sub-components:

packages/mermaid/src/diagrams/er/parser/erDiagram.jison

@@ -94,6 +94,22 @@ start
     : 'ER_DIAGRAM' document 'EOF' { /*console.log('finished parsing');*/ }
     ;
 
+relationship
+  : ENTITY relationType ENTITY maybeRole
+    {
+      yy.addRelationship($1, $4, $3, $2);
+    };
+
+maybeRole
+  : COLON role
+    {
+      $$ = $2;
+    }
+  | /* empty */
+    {
+      $$ = '';
+    };
+
 document
 	: /* empty */ { $$ = [] }
 	| document line {$1.push($2);$$ = $1}
@@ -108,32 +124,34 @@ line
 
 
 statement
-    : entityName relSpec entityName COLON role
+    : entityName relSpec entityName maybeRole
       {
           yy.addEntity($1);
           yy.addEntity($3);
-          yy.addRelationship($1, $5, $3, $2);
+          yy.addRelationship($1, $4, $3, $2);
       }
-    | entityName STYLE_SEPARATOR idList relSpec entityName STYLE_SEPARATOR idList COLON role
+    | entityName STYLE_SEPARATOR idList relSpec entityName STYLE_SEPARATOR idList maybeRole
+
       {
           yy.addEntity($1);
           yy.addEntity($5);
-          yy.addRelationship($1, $9, $5, $4);
+          yy.addRelationship($1, $8, $5, $4);
           yy.setClass([$1], $3);
           yy.setClass([$5], $7);
       }
-    | entityName STYLE_SEPARATOR idList relSpec entityName COLON role
+    | entityName STYLE_SEPARATOR idList relSpec entityName maybeRole
+
       {
           yy.addEntity($1);
           yy.addEntity($5);
-          yy.addRelationship($1, $7, $5, $4);
+          yy.addRelationship($1, $6, $5, $4);
           yy.setClass([$1], $3);
       }
-    | entityName relSpec entityName STYLE_SEPARATOR idList COLON role
+    | entityName relSpec entityName STYLE_SEPARATOR idList maybeRole
       {
           yy.addEntity($1);
           yy.addEntity($3);
-          yy.addRelationship($1, $7, $3, $2);
+          yy.addRelationship($1, $6, $3, $2);
           yy.setClass([$3], $5);
       }
     | entityName BLOCK_START attributes BLOCK_STOP

packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js

@@ -981,6 +981,12 @@ describe('when parsing ER diagram it...', function () {
       expect(rels[0].roleA).toBe('places');
     });
 
+    it('should allow label as optional', function () {
+      erDiagram.parser.parse('erDiagram\nCUSTOMER ||--|{ ORDER');
+      const rels = erDb.getRelationships();
+      expect(rels[0].roleA).toBe('');
+    });
+
     it('should represent parent-child relationship correctly', function () {
       erDiagram.parser.parse('erDiagram\nPROJECT u--o{ TEAM_MEMBER : "parent"');
       const rels = erDb.getRelationships();
@@ -989,6 +995,20 @@ describe('when parsing ER diagram it...', function () {
       expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.MD_PARENT);
       expect(rels[0].relSpec.cardA).toBe(erDb.Cardinality.ZERO_OR_MORE);
     });
+
+    it('should handle whitespace-only relationship labels', function () {
+      erDiagram.parser.parse('erDiagram\nBOOK }|..|{ AUTHOR : "   "');
+      let rels = erDb.getRelationships();
+      expect(rels[rels.length - 1].roleA).toBe('   ');
+
+      erDiagram.parser.parse('erDiagram\nBOOK }|..|{ GENRE : "\t"');
+      rels = erDb.getRelationships();
+      expect(rels[rels.length - 1].roleA).toBe('\t');
+
+      erDiagram.parser.parse('erDiagram\nAUTHOR }|..|{ GENRE : "      "');
+      rels = erDb.getRelationships();
+      expect(rels[rels.length - 1].roleA).toBe('      ');
+    });
   });
 
   describe('prototype properties', function () {

packages/mermaid/src/docs/syntax/entityRelationshipDiagram.md

@@ -89,6 +89,30 @@ erDiagram
     "This **is** _Markdown_"
 ```
 
+#### Optional Relationship Labels
+
+Starting from Mermaid version 11.11.0, the relationship label in ER diagrams is optional. You can define relationships without specifying a label, and the diagram will render correctly.
+
+For example, the following is valid:
+
+```mermaid-example
+erDiagram
+    BOOK }|..|{ AUTHOR
+    BOOK }|..|{ GENRE
+    AUTHOR }|..|{ GENRE
+```
+
+This will show the relationships between the entities without any labels on the connecting lines.
+
+You can still add a label if you want to describe the relationship:
+
+```mermaid-example
+erDiagram
+    BOOK }|..|{ AUTHOR : written_by
+    BOOK }|..|{ GENRE : categorized_as
+    AUTHOR }|..|{ GENRE : specializes_in
+```
+
 ### Relationship Syntax
 
 The `relationship` part of each statement can be broken down into three sub-components: