LLD Sample

Low-level design :  (LLD) is a component-level design process that follows a step-by-step refinement process. This process can be used for designing data structures, required software architecture, source code and ultimately, performance algorithms.

Requirements : Need to define requirements for what we need to make.
Eg: We need to take and store users' info in our project.

Implementation :

• At DB Level : 

  • We need to make one collection in our DB

  • Need to define all fields and data types. For eg
    Id : type will be base64 string
    email : type will be string
    first_name : type will be string
    last_name : type will be string

• At Code level:

  • We need to make one EndPoint where we will write the apis,

  • We will make five apis.

• Get api to get the list of users from users table.

  • Happy Flow : The case when you get the response successfully.

    • Request will go to controller, then controller will call service layer, in service layer system will check data in cache, if values will present in cache then service will send response to controller after getting data from cache otherwise service layer will call dao layer for data, dao layer will get data from DB and send to service layer, service layer will send response to controller and controller will send response to client.

      URL : {baseURL}/api/v1/users?page=1&per_page=10 Method : GET Response body: (Http Status will be 200) { “data” : [ { “Id” : “afsfsf345gd”, “email” : “abc@yopmail.com”, “first_name” : “abc”, “last_name” : “bcd” }, { “Id” : “afsfsf345gdsdfds”, “email” : “abcd@yopmail.com”, “first_name” : “abcd”, “last_name” : “bcde” } ], "total": 2, "page": 1, "per_page": 10 }

• Get api to get the list of users from users table.

  • Happy Flow : The case when you get the response successfully for given Id.

    • Request will go to controller, then controller will call service layer, in service layer system will check data in cache, if values will present in cache then service layer will get the records then find for particular id and send response to controller otherwise service layer will call dao layer for data, dao layer will get data from DB and send to service layer, service layer will send response to controller and controller will send response to client.

      URL : {baseURL}/api/v1/users/afsfsf345gdsdfds Method : GET Response body: (Http Status will be 200) { “data” : [ { “Id” : “afsfsf345gd”, “email” : “abc@yopmail.com”, “first_name” : “abc”, “last_name” : “bcd” }, { “Id” : “afsfsf345gdsdfds”, “email” : “abcd@yopmail.com”, “first_name” : “abcd”, “last_name” : “bcde” } ], "total": 2, "page": 1, "per_page": 10 }

  • Failed due to not found :

    • When system will not get any object for given id.

      Response body: (status code will be 404) { “message“ : “No user found“ }

• Post api to save the new entity in user table.

  • Happy Flow : The case when you saved new entity in DB successfully.

    • Request will go to controller, then controller will call service layer and service layer will call dao layer to save the entity, then service layer will update the cache for users list and send response to controller and controller will send response to client.

      URL : {baseURL}/api/v1/users Method : POST Requesy body: { “email” : “newUser@yopmail.com”, “first_name” : “new”, “last_name” : “user” } Response body: (Http Status will be 201) { “id” : “sdfsfa0398j”, “email” : “newUser@yopmail.com”, “first_name” : “new”, “last_name” : “user” }

  • Failed at request validation : Reasons that could lead to failure at request validation

    • Email already exists

      Response Body: (status code will be 403) { “message“ : “email already exists“ }

    • first_name of the user can not be more than 50 characters

      Response Body: (status code will be 400) { “message“ : “first_name of the user can not be more than 50 characters“ }

    • Field must be required

      Response Body: (status code will be 400) { “message“ : “email must be required“ }

• Put api to update the existing entity.

  • Happy Flow : The case when you updated the entity in DB successfully.

    • Request will go to controller, then controller will call service layer, service layer will call dao layer to update the entity, then service layer will update the cache for users list and send response to controller and controller will send response to client.

      URL : {baseURL}/api/v1/users/{id} Method : PUT Request Body: { “first_name” : “new”, “last_name” : “name” } Response Body: (Http Status will be 200) { “Id” : “3oiuo3j4oj3oj43”, “email” : “newUser@yopmail.com”, “first_name” : “new”, “last_name” : “name” }

  • Failed at request validation : Reasons that could lead to failure at request validation

    • first_name of the user can not be more than 50 characters

      Response Body: (status code will be 400) { “message“ : “first_name of the user can not be more than 50 characters“ }

• Delete api to delete the entity.

  • Happy Flow : The case when you deleted the entity in DB successfully.

    • Request will go to controller, then controller will call service layer, service layer will call dao layer to delete the entity, then service layer will update the cache for users list and send response to controller and controller will send response to client.

      URL : {baseURL}/api/v1/users/{id} Method : Delete Response Body: (status code will be 200) { “message” : “User deleted successfully.” }

  • Failed at request validation : Reasons that could lead to failure at request validation

    • When system will not get any object for given id.

      Response body: (status code will be 404) { “message“ : “No user found“ }

Performance : We need to define how we will increase our apis performance. For eg:

• We have to define what kind of cache we are going to use for fast retrieval.

• We must reduce extra db calls and iterations.
  
  

Impact on other modules : we have to check if our current changes are making any impact on existing modules.