docs: document composite indices + primary key changes (#7902)

www/apps/book/app/advanced-development/data-models/relationships/page.mdx

@@ -31,12 +31,12 @@ export const oneToOneHighlights = [
 import { model } from "@medusajs/utils"
 
 const User = model.define("user", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   email: model.hasOne(() => Email),
 })
 
 const Email = model.define("email", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   user: model.belongsTo(() => User, {
     mappedBy: "email",
   }),
@@ -70,12 +70,12 @@ export const oneToManyHighlights = [
 import { model } from "@medusajs/utils"
 
 const Store = model.define("store", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   products: model.hasMany(() => Product),
 })
 
 const Product = model.define("product", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   store: model.belongsTo(() => Store, {
     mappedBy: "products",
   }),
@@ -101,12 +101,12 @@ export const manyToManyHighlights = [
 import { model } from "@medusajs/utils"
 
 const Order = model.define("order", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   products: model.manyToMany(() => Product),
 })
 
 const Product = model.define("product", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   order: model.manyToMany(() => Order),
 })
 ```
@@ -132,14 +132,14 @@ export const relationNameHighlights = [
 import { model } from "@medusajs/utils"
 
 const User = model.define("user", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   email: model.hasOne(() => Email, {
     mappedBy: "owner",
   }),
 })
 
 const Email = model.define("email", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   owner: model.belongsTo(() => User, {
     mappedBy: "email",
   }),
@@ -170,7 +170,7 @@ export const highlights = [
 import { model } from "@medusajs/utils"
 
 const Store = model.define("store", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   products: model.hasMany(() => Product),
 })
 .cascades({
@@ -178,7 +178,7 @@ const Store = model.define("store", {
 })
 
 const Product = model.define("product", {
-  id: model.id(),
+  id: model.id().primaryKey(),
   store: model.belongsTo(() => Store, {
     mappedBy: "products",
   }),