Manju

Greetings! In this third installment of our simple NgRx series we are going to have a look at selectors. As this is again confusing at first, let's use our simple message string to learn this. For the simplicity, i'm not using any actions in this example. Comple code can is here  https://github.com/slmanju/ngrx-at-slmanju/tree/main/ngrx-hello-selector What we need Store initial value Create reducer to get initial value Register the reducer Create selector(s) Read, change values from the component Generate the Project ng new ngrx-hello-selector --routing=false --style=css cd ngrx-hello-selector/ ng add @ngrx/store@latest ng serve Register the Reducer As in our first article, we will just store a string value in our store. Then register the reducer to read it. If you haven't read it, here is the code. ngrx-hello-selector/src/app/app.reducer.ts const initialState = 'Whatever you are, be a good one.'; const _messageReducer = createReducer( ini...

Greetings! This is our second article on our simple NgRx series. As we saw how to read stored value from the Store, let's see how we can change the value using Actions in this article. Yet again, this will be another simple working example. Full working example https://github.com/slmanju/ngrx-at-slmanju/blob/main/ngrx-hello-action "Red Light, Green Light" ;) What we need Store initial value Define actions to change it Create reducers to react on the action changes Register the reducer Read, change values Generate the Project ng new ngrx-hello-action --routing=false --style=css cd ngrx-hello-action/ ng add @ngrx/store@latest ng serve As this is to demonstrate, we will add Store realted code in a single file. Initial Value In this example, we will store color value and change it. export const initialState: string = 'red'; Create Action Let us create our red and green actions. export const red = createAction('[Color] Red'); export ...

Greetings! When learning Angular, one of the difficulties we face (including myself) is understanding NgRx. In theory, it is so simple. However, difficulty is in implementation. I don't want to add lengthy explanations (documentation has better explanation anyway) but want to add simplest working examples incrementatly so that anyone in any level can understand. As usual, here is the code https://github.com/slmanju/ngrx-at-slmanju/tree/main/ngrx-hello-store Let's create the most simplest store then :). A simple value stored in the store!!! What we need Store with initial value A reducer A component to read the value Yes, no action, no effects as this example is so simple. Generate the Project ng new ngrx-hello-store --routing=false --style=css cd ngrx-hello-store/ ng add @ngrx/store@latest ng serve Initiate the Reducer We will store a simple message in our store. ngrx-hello-store/src/app/hello.reducer.ts import { Action, createReducer } from '@...

Greetings! If you have used RDBMS like MySQL or Oracle you know that those databases support auto-increment fields or sequences. However MongoDB's way of ID is using an ObjectId which is a large string. However if you want an unique sequence what will you do? One solution is of cause to use RDBMS solution like Oracle. Unlike NoSQL solutions, RDBMS have problems with scaling. Let's imagine that to overcome scaling problems we are using MongoDB. Why do we need a unique sequence? We will need unique sequences for several reasons. Design a hit counter. Short string generation (https://www.slmanju.com/2021/07/basebase62-encoding-with-java.html). Rate limiting. Easy to read identifier value. You are migrating from relational database. Eventhough MongoDB doesn't offer this feature out of box, we can implement it using it's atomic operations. The trick is to create a collection with desired name as the _id and findAndModify with $inc. db.counters.insert({ _id: "my-se...

Greetings! Converting base 10 number to another base is a common mathematical operation. First of all, why do we need base62? Shorten a given URL Saving a file using timestamp Short text As the base62 has lot more characters, we can easily create a small version of a given number. Let's do the Math Converting to another base has common steps. ( base-10-to-other-bases ) Divide the number by the base and get the remainder. Divide the quotient and get the remainder. Continue this process untill the quotient is zero. Order the remainders from last to first. We can try this process for hexa-decimal. As hexa-decimal is 16 chars, we need a way to represent that value. For that 0123456789ABCDEF are used. 42 42 / 16 = remainder 10, quotient 2 2 / 16 = remainder 2, quotient 0 Since 10 is A in hexa representation 42 = 2A in hexa-decimal number system. This same logic is applied for Base62. We can use 0-9A-Za-z characters to encoe base62. 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopq...