DEV Community: Keval Domadia

Understanding HQL from Zero to Hero!

Keval Domadia — Tue, 14 Mar 2023 11:03:46 +0000

To Create data:

String hql = "INSERT INTO Question(title, topic_id, answer) VALUES(:title, :topic_id, :answer)";
Query query = session.createQuery(hql);
query.setParameter("title", "What is life and universe?");
query.setParameter("topic_id", 42);
query.setParameter("answer", "Discovery");
int result = query.executeUpdate();

To Read data:

To List data - as in multiple rows.

String hql = "FROM Question WHERE topic_id > :topic_id";
Query query = session.createQuery(hql);
query.setParameter("topic_id", 42);
List<Question> questions = query.list();

Notice: .list()

Question object assumes the table is called questions.

To List data - as in a single row.

String hql = "FROM Question WHERE topic_id > :topic_id";
Query query = session.createQuery(hql);
query.setParameter("topic_id", 42);
List<Question> singleQuestion = query.uniqueResult();

However, IF it is not unique as in key unique, which would be the case in list of Topics.

Use the list() but also use setMaxResult(). Example:

String hql = "FROM Question WHERE topic_id > :topic_id";
Query query = session.createQuery(hql);
query.setParameter("topic_id", 42);
query.setMaxResult(1);
List<Question> singleQuestion = query.uniqueResult();

Incase you are fetching data in a paginated fashion, example page 2 will show results from 20 to 30
then use the above in combination with setFirstResult(20) with setMaxResult(10). Take it that setMaxResult is LIMIT in SQL and setFirstResult is OFFSET.

To Update:

String hql = "UPDATE Question SET topic_id = :topic_id WHERE id = :id";
Query query = session.createQuery(hql);
query.setParameter("id", 1);
query.setParameter("topic_id", 42);
int result = query.executeUpdate();

To Delete:

String hql = "DELETE FROM Question WHERE id = :id";
Query query = session.createQuery(hql);
query.setParameter("id", 1);
int result = query.executeUpdate();

Hope it helps.!

Difference between yield and await in Dart / Flutter

Keval Domadia — Sun, 19 Feb 2023 05:41:01 +0000

In summary:
yeild is used under the context of a Business Logic Component or BLoC and await is used under the context of a Future.

The yield keyword is used in a Dart generator function to return a value from the function and pause the function's execution until the next value is requested. In a Bloc, the yield keyword is used to emit a new state from the mapEventToState function in response to an event.

mapEventToState is a method in a Bloc class that maps an incoming event to a new state. It takes an event as an input and returns a state as an output. In a Bloc, the mapEventToState method is responsible for converting incoming events into new states, which can be emitted using the yield keyword. For example, in the code mapEventToState(event), the mapEventToState method is called with the event object as an argument, and it returns a new state based on the type of the event. The new state can then be emitted using the yield keyword, and it will be passed to the BlocBuilder widget to update the UI.

If you have any questions, you know where to find me.

Get good. Be good. Code hard! Cheers!

Understanding useEffect with useState easily

Keval Domadia — Wed, 15 Feb 2023 05:55:47 +0000

I have often been asked how to create a placeholder effect whilst the data is being fetched.

When you add a placeholder to the content, the user gets a feeling that the data is 'almost' loaded now.

I am writing this blog for my students to follow up incase they need a ready reference to check.

You need to 2 things. useState and useEffect

useEffect is a function that is used to manage side effects in your components. Side effects are things that your component needs to do that are not related to rendering content on the screen, such as fetching data from an API.

The best way to use useEffect() is in combination of useState().

Let me get down to the code to explain better. Check this out:

import React, { useState, useEffect } from 'react';
import { Text, View } from 'react-native';

function MyComponent() {
  const [data, setData] = useState(false);

  useEffect(() => {
    fetch('https://example.com/api/getdata')
      .then(response => response.json())
      .then(data => setData(data));
  }, []);

  return (
    <View>
      {data ? <Text>{data}</Text> : <Text>Loading...</Text>}
    </View>
  );
}

Now following this...

under View I have added a ternary operator to check if the data is true or false. By default it is false, thus the user will see loading...

When the useEffect reaches the second then, that is, processed json, it will set state of the data with the data from the API. This making it false-positive, or a True.

Alternatively, we can also create another state which changes and uses absolute True and False

To do that, check the code below:

import React, { useState, useEffect } from 'react';
import { Text, View } from 'react-native';

function MyComponent() {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch('https://example.com/api/getdata')
      .then(response => response.json())
      .then(data => {
        setData(data);
        setLoading(false);
      });
  }, []);

  return (
    <View>
      {loading ? (
        <Text>Loading...</Text>
      ) : (
        <Text>{data}</Text>
      )}
    </View>
  );
}

This puts loading as a boolean with either a true or a false, instead of false and true-y.

Hope this helps.

If you have more questions, you know where to reach me!

Be good. Get Good. Have fun!