docs: general fixes and overall changes (#7258)

* editing halfway

* edited second half

* adjust starter steps

* fix build

* typo fix

www/apps/book/app/advanced-development/modules/database-operations-in-services/page.mdx

@@ -4,68 +4,19 @@ export const metadata = {
 
 # {metadata.title}
 
-In this document, you’ll learn how to implement database operations, such as creating a record, in a service’s methods.
+In this document, you’ll learn how to implement database operations, such as creating a record, in the main service.
 
-## Transaction Manager
+## Use Data Model Services
 
-A transaction wraps a set of database operations to ensure that when an error occurs, all database changes made by the executed operations are rolled back.
-
-When you implement a method in your service, you must add the `@InjectTransactionManager` decorator to the method performing database operations. For example:
-
-```ts title="src/modules/hello/service.ts" highlights={[["26"]]}
-// other imports
-import { InjectTransactionManager } from "@medusajs/utils"
-import { DAL } from "@medusajs/types"
-
-type InjectedDependencies = {
-  baseRepository: DAL.RepositoryService
-  myCustomService: ModulesSdkTypes.InternalModuleService<any>
-}
-
-class HelloModuleService extends ModulesSdkUtils
-  .abstractModuleServiceFactory<
-    // ...
-  >(
-    // ...
-  ) {
-    protected baseRepository_: DAL.RepositoryService
-
-    constructor(
-      { baseRepository }: InjectedDependencies
-    ) {
-      // @ts-ignore
-      super(...arguments)
-      this.baseRepository_ = baseRepository
-    }
-
-    @InjectTransactionManager("baseRepository_")
-    async create(
-      // TODO add parameters
-    ) {
-      // TODO add implementation
-    }  
-}
-```
-
-The `@InjectTransactionManager` decorator accepts as a parameter the name of the service class field to inject the transaction manager to, which is the `baseRepository_` field.
-
----
-
-## Generated Service Methods
-
-As mentioned in a previous chapter, when you use the container loader factory to register resources in your module’s container, the factory creates a service for each data model you specify and registers it in the container. The registration name is the camel-case name of the data model with `Service` appended to it.
-
-So, the container loader factory creates a `myCustomService` for the `MyCustom` data model.
-
-These generated services already implement data-management methods such as `create` or `update`. So, in your module’s service, you can resolve the generated service and use it to create a record.
+The module container has a generated service registered for each data model. You can resolve that service and use it to perform database operations on the data model.
 
 For example:
 
 export const highlights = [
   ["13", "", "Inject myCustomService, which is the service generated by the container loader for the MyCustom data model."],
-  ["23", "", "Add a new field for the generated service of the MyCustom data model."],
-  ["31", "", "Set the class field to the injected dependency."],
-  ["39", "create", "Use the `create` method of the generated service."]
+  ["22", "", "Add a new field for the generated service of the MyCustom data model."],
+  ["29", "", "Set the class field to the injected dependency."],
+  ["35", "create", "Use the `create` method of the generated service."]
 ]
 
 ```ts title="src/modules/hello/service.ts" highlights={highlights}
@@ -75,12 +26,12 @@ import { MyCustom } from "./models/my-custom"
 
 // ...
 
+// recommended to define type in another file
 type CreateMyCustomDTO = {
   name: string
 }
 
 type InjectedDependencies = {
-  baseRepository: DAL.RepositoryService
   myCustomService: ModulesSdkTypes.InternalModuleService<any>
 }
 
@@ -90,22 +41,18 @@ class HelloModuleService extends ModulesSdkUtils
   >(
     // ...
   ) {
-    protected baseRepository_: DAL.RepositoryService
     protected myCustomService_: ModulesSdkTypes.InternalModuleService<MyCustom>
 
     constructor(
-      { baseRepository, myCustomService }: InjectedDependencies
+      { myCustomService }: InjectedDependencies
     ) {
       // @ts-ignore
       super(...arguments)
-      this.baseRepository_ = baseRepository
       this.myCustomService_ = myCustomService
     }
 
-    @InjectTransactionManager("baseRepository_")
     async create(
-      data: CreateMyCustomDTO,
-      @MedusaContext() context: Context = {}
+      data: CreateMyCustomDTO
     ): Promise<MyCustomDTO> {
       const myCustom = await this.myCustomService_.create(
         data, 
@@ -117,6 +64,6 @@ class HelloModuleService extends ModulesSdkUtils
 }
 ```
 
-In the above example, you add `myCustomService` to the `InjectedDependencies` type to resolve the service in the constructor and set it in a class field.
+In the above example, you resolve `myCustomService` in the main service's constructor. The `myCustomService` is the generated service for the `myCustom` data model.
 
-In the `create` method, you use `myCustomService`'s `create` method to create the record. You pass it the record’s data as a first parameter, and the Medusa application’s context as a second parameter.
+Then, in the `create` method of the main service, you use `myCustomService`'s `create` method to create the record.