Understanding and Implementing Schemas in Python

-
Understanding and Implementing Schemas in Python Introduction In the world of programming, particularly in the context of data management and validation, schemas play a vital role. A schema is essentially a blueprint or a predefined structure that defines the expected format, data types, and constraints for a given data entity. In this blog, we will delve into the concept of schemas in Python, exploring what they are, why they are important, and how you can implement them in your projects. What is a Schema? A schema serves as a contract between different components of a system, ensuring that data is consistent, valid, and well-structured. It defines the rules for how data should be organized, what fields it should contain, and what types of values those fields can hold. In essence, a schema acts as a set of rules that data must adhere to in order to be considered valid. Why Are Schemas Important? Data Validation: Schemas provide a way to validate incoming data. When data is received o...
Post a Comment

aliased function in flask, python and SQLAlchemy

-
aliased function in flask, python and SQLAlchemy


SQLAlchemy is a powerful and flexible ORM (Object-Relational Mapping) tool for Python that allows developers to interact with databases in a more object-oriented manner. One of the most useful features of SQLAlchemy is the ability to create aliases of database tables using the aliased function. In this blog post, we will explore the aliased function and how it can be used to simplify database queries.

What is Aliased?

The aliased function in SQLAlchemy allows you to create an alias for a table or subquery in a SQL statement. The alias is essentially a new reference to the same table or subquery, but with a different name that can be used in place of the original name in the SQL statement. The aliased function returns a new Alias object, which is a lightweight representation of the aliased table or subquery.

Using Aliased

Let's take a look at a simple example to demonstrate how the aliased function works. Suppose we have a database table called users that contains user information such as id, name, email, and phone. We also have a second table called orders that contains order information such as id, user_id, product, and quantity. We want to write a query that retrieves the names of all users who have placed an order for a specific product. Here is how we can use aliased to accomplish this:

from sqlalchemy.orm import aliased from myapp.models import User, Order, db # Create an alias for the Order table OrderAlias = aliased(Order) # Build the query using the aliased table query = db.session.query(User.name)\ .join(OrderAlias, User.id == OrderAlias.user_id)\ .filter(OrderAlias.product == 'Widget')\ .distinct() # Execute the query and retrieve the results results = query.all()

In this example, we create an alias for the Order table using the aliased function and give it the name OrderAlias. We then join the User and OrderAlias tables on the id and user_id columns, respectively, and filter the results to only include orders for the product 'Widget'. Finally, we retrieve the distinct names of the users who have placed orders for the specified product.

Benefits of Using Aliased

The use of aliases can greatly simplify complex SQL statements and make them more readable. Aliases can be especially useful when working with self-referential or recursive relationships in a database, where the same table is referenced multiple times in a query. By creating aliases for the same table with different names, developers can avoid naming conflicts and make the SQL statement easier to understand.

Conclusion

The aliased function in SQLAlchemy is a powerful tool that can simplify database queries by allowing developers to create aliases of tables and subqueries. This can make SQL statements more readable and easier to understand, especially when working with complex relationships between tables. By using aliased, developers can take advantage of the full power and flexibility of SQLAlchemy to interact with databases in a more object-oriented way.


Happy Learning!! Happy Coding!!

Comments

New comments are not allowed.

Popular posts from this blog

useNavigate and useLocation hooks react-router-dom-v6

-
Image
useNavigate and useLocation hooks - Navigating programmatically to a route. In this post, we will learn about two new hooks from react-router-dom version 6 library. 1) useNavigate - Let’s say on click of a button, If you want to perform redirection to the page, then react router provide us with a hook called as useNavigate. - useNavigate hook replaced useHistory hook, but it works same as useHistory but in addition it has good feature. - useNavigate hook is only available in react-router-dom version 6. - We can redirect to Previous and Next page with the help of useNavigate hooks.  2) useLocation - We required two library React 16.8+ and react-router-dom 5.1+ for useLocation hook. - It is a function that returns the location object that contains information about the current URL. - New location object is created, whenever the URL changed. useNavigate and useLocation hooks react router dom version 6Js and Xstate Install React Router Command npm install react-router-dom --save Sample...
Read more

Localization in React Js

-
Image
Localization in React Js using react-localization package. In this post, we will learn about Localization in React Js. Now a day, Localization is very important and basic requirement in every web based application. Following source code will help you, creating a multilingual Web application in React Js. Note: Use Double Click for Radio Boxes. Localization in React Js Installation: npm install --save react-localization Folder Structure: Sample Code A) index.js import   React   from   "react" ; import   ReactDOM   from   "react-dom" ; import   App   from   "./App" ; ReactDOM . render ( < App   /> ,  document . getElementById ( "root" )); B) App.js ( Class Component ) import   React , {  Component  }  from   'react' ; import   labels   from   './Local/localize' ; import   './style.css' ; class   App   extends   Component  {    constructor ( props )...
Read more

How to implement error boundaries in React Js

-
Error boundaries in React Js In this post, we will learn about "Error Boundaries in React Js". First of all, why we required Error Boundaries? This is the first question comes in my mind, as before React 16, we don't have any mechanism to catch error inside components and because of which whole app in broken state on next renders. No ways to handle these errors in React Components, nor it gives any methods to recover from them. React 16 introduces a new concept to handle such errors by using the error boundaries. So now, if any error found in a part of the UI, it does not break the whole application. According to official document of React Js, There are following few areas in application, where error boundaries are not suitable solution. a) Event handlers b) Asynchronous code (e.g., setTimeout) c) Server-side rendering d) Errors are thrown in the error boundary itself  For complex application which contains multiple components, we can declare multiple error boundaries to ...
Read more

Pass data from child component to its parent component in React Js

-
Image
Pass data from child component to its parent component in React Js In this post, we will learn about how to pass data from child component to its parent component in React js. We need to do following steps to pass/send data from child component to parent component: a) In the parent component, create a callback function. This callback function is useful to retrieve the data from the child component. b) Pass the callback function to the child as a props from the parent component. c) The child component calls the parent callback function using props and sends the data to the parent component. Send data from child component to its parent component Sample Code: A) index.js import   React   from   "react" ; import   ReactDOM   from   "react-dom" ; import   App   from   "./App" ; ReactDOM . render ( < App   /> ,  document . getElementById ( "root" )); B) App.js import   React , {  useState  }  from   're...
Read more

Create a Shopping Item App using React Js and Xstate

-
Image
Create a Shopping Item App using React Js and Xstate ( state management )  In this post, we will create a shopping item app using React js and Xstate. Generally, we use redux for state management but in this application, I am going to show you state management with the help of Xstate. Shopping Item App using React Js and Xstate Dependency:   npm install xstate @xstate/react Folder Structure: Sample Code: A) index.js import   React   from   "react" ; import   ReactDOM   from   "react-dom" ; import   App   from   "./App" ; ReactDOM . render ( < App   /> ,  document . getElementById ( "root" )); B) App.js import   React   from   'react' ; import   Product   from   './Product/Product' ; import   './style.css' ; import  { ShoppingContext ,  ShoppingMachine }  from   './State/index' import  {  useMachine  }  from   '@xstate/react' ; export ...
Read more

How to fetch data using Axios Http Get Request in React Js?

-
Image
How to fetch data using  Axios - Http Get Request in React Js? In one of my previous post, I had explained all about Fetch() method to retrieve data from api server. In this post, I am going to demystify how to achieve same thing using axios. Axios has many advantages over fetch() method. 1) Axios has the ability to intercept HTTP request. 2) With axios.all() method, you can make simultaneous requests, simply send an array of request to this method, then use axios.spread() method to assign the properties of the response array to separate varialbes. 3) Axios automatically stringifies the data when sending requests, as in fetch() method, you would have to do it manually. 4) You can set response timeout. 5) Support backward compatibility, this is because it uses XMLhttprequest under the hood.  Fetch User Data Using Axios - Get Request Installation: npm install axios or yarn add axios Sample Code: A) index.js import   React   from   "react" ; import   ReactDOM...
Read more

How to fetch data from an API using fetch() method in React Js

-
Image
How to fetch data from an API using fetch() method in React Js? Now a day, we can't imagine web application without API so one of the basic requirement of any web application is to communicate with servers through HTTP protocol. This can be easily done using Fetch and Axios .  In this post, we are mainly focusing on Fetch. The Fetch API provides a fetch() method defined on the window object. The fetch method has one mandatory argument i.e., URL of the resource to be fetched. This method returns promise object that can be used to retrieve response of the request.  There are following limitations of Fetch API: a) Fetch does not allows cancelling request and request timeout. b) Fetch does not provide a way to intercept HTTP requests. c) Fetch has no url in request object. d) No installation is required. e) Fetch does not have XSRF protection. f) Fetch uses the body property. g) Fetch is a two step process when handling JSON data, first - to make actual request. second - to call j...
Read more

Create a ToDo App in React Js | Interview Question

-
Image
Create a ToDo App in React Js | Interview Question In this post, you will learn about how to create To-Do App in React using hooks. I have use arrays of object to save to do list, not redux and required some basic packages like Node and npm. Following is the UI functionality of the application. Todo App in React Js Componets:     There are four component created in our application.    a) ToDoHeader: Created for showing details of Header section.    b) AddToItem: Created for adding text to "ToDo list".    c) AddToDoList: Created for showing "ToDo list".    d) ToDoFooter: Created for showing details of Footer section. Sample Code: 1) App.js import   React , {  useState  }  from   'react' ; import   './style.css' ; window . id  =  0 ; const   ToDoHeader  = ()  =>  {    return   < div   id = "todoHeader" >  To Do Applica...
Read more

Routing in React using React-Router Version 6

-
Image
 Routing in React using React-Router Version 6 What is Routing? - The process of navigating a user to different pages based on their request is known as routing. - Routing is a process of binding a web URL to specific resource. In react we can say, "it is a binding of URL to a specific component. - As react is a user interface library, it does not support routing. - In this post, we will learn about "routing in react using  react-router-dom  library version 6". Install React Router Command npm install react-router-dom --save Main component used for Navigation 1) BrowserRouter as Router - top level component  2) Routes - Replacement of Switch component. 3) Route - child component of Routes, useful for mapping a specific URL to a component. 4) Link - Similar to anchor tag in html. Note:  Switch Component is deprecated from version 6. The new component is introduced called as  Routes . Multiple Routing in React Js Installation:  npm install react-router-d...
Read more

Auto Increment, Decrement, Reset and Pause counter in React Js | Interview Question

-
Image
Auto Increment, Decrement, Reset & Pause counter in React Js | Interview Question In this post, I am going to cover one interview question & following is the functionality of the application. I hope you may have come across such situation especially in react interview. Counter in React Js There are four functionality covered in the application: A) Increment B) Decrement C) Reset D) Pause Sample Code: A) App.js import   React , {  useState ,  useEffect  }  from   'react' ; import   './style.css' ; export   default   function   App () {    const  [ count ,  setCount ] =  useState ( 0 );    const  [ action ,  setAction ] =  useState ( false );    const  [ operation ,  setOperation ] =  useState ( '' );    useEffect (()  =>  {      if  ( action ) {      ...
Read more