Sublevel-prefixer: Prefix A Key with A Sublevel Prefix

sublevel-prefixer

Prefix a key with a sublevel prefix

npm install sublevel-prefixer

Usage

var prefixer = require('sublevel-prefixer')
var prefix = prefixer('!') // use '!' as the separator

// using string keys
console.log(prefix('my-prefix', 'my-key')) // !my-prefix!my-key

// using binary keys
console.log(prefix('my-prefix', new Buffer('my-key'))) // returns above as a buffer

Author: Mafintosh
Source Code: https://github.com/mafintosh/sublevel-prefixer 
License: MIT license

#javascript #prefix #key 

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Sublevel-prefixer: Prefix A Key with A Sublevel Prefix

sublevel-prefixer

Prefix a key with a sublevel prefix

npm install sublevel-prefixer

Usage

var prefixer = require('sublevel-prefixer')
var prefix = prefixer('!') // use '!' as the separator

// using string keys
console.log(prefix('my-prefix', 'my-key')) // !my-prefix!my-key

// using binary keys
console.log(prefix('my-prefix', new Buffer('my-key'))) // returns above as a buffer

Author: Mafintosh
Source Code: https://github.com/mafintosh/sublevel-prefixer 
License: MIT license

#javascript #prefix #key 

Java: How to Get Keys and Values from a Map

Introduction

Key-value stores are essential and often used, especially in operations that require fast and frequent lookups. They allow an object - the key - to be mapped to another object, the value. This way, the values can easily be retrieved, by looking up the key.

In Java, the most popular Map implementation is the HashMap class. Aside from key-value mapping, it’s used in code that requires frequest insertions, updates and lookups. The insert and lookup time is a constant O(1).

In this tutorial, we’ll go over how to get the Keys and Values of a map in Java.

#java #java: how to get keys and values from a map #keys #map #values #how to get keys and values from a map

How to Sort a HashMap by Key in Java

In this tutorial, we’ll take a look at how to sort a HashMap by key in Java.

Let’s go ahead and create a simple HashMap:

Map<String, Integer> unsortedMap = new HashMap();

unsortedMap.put("John", 21);
unsortedMap.put("Maria", 34);
unsortedMap.put("Mark", 31);
unsortedMap.put("Sydney", 24);

unsortedMap.entrySet().forEach(System.out::println);

We’ve got Strings as keys, and Integers as values. Most of the time, you’ll encounter Integers or Strings as keys, and custom objects, Strings or Integers as values. We’ll want to sort this HashMap, based on the String keys.

HashMaps don’t guarantee to maintain the order of its elements in any case. The order can change through time, and they most definitely won’t be printed back in the order of insertion:

John=21
Mark=31
Maria=34
Sydney=24

If you re-run this program, it’ll keep this order, since HashMaps order their elements into bins, based on the hash value of the keys. When printing values from a HashMap, its contents are printed sequentially, so the results will stay the same if we re-run the program multiple times.

#java #how to sort a hashmap by key in java #hashmap #key in java #sort #sort a hashmap by key in java

What are API Keys? and using API Keys

In this video, we use New York’s MTA Bus Time API in order to find bus stops near a given location and determine when a specific bus arrives at a given stop. This API requires an API Key and in this tutorial, we’ll look at what that means and how to affects your http request. Thank you for watching and happy coding!

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#api #api keys #what are api keys

SQL Primary Key Example | Primary Key in SQL Tutorial

SQL primary key is a field in a table that is used for uniquely identifying a row in a table. If the column has a primary key constraint, then it will contain unique values and will not able to contain any NULL values. A primary key length cannot exceed more than 900 bytes.

SQL PRIMARY KEY

SQL PRIMARY KEY constraint uniquely identifies each row in the table. Primary keys must contain UNIQUE values, and cannot contain the NULL values. The table can have only ONE primary key; and in the table, that primary key can consist of the single or multiple columns (fields).

A  table will contain only one primary key, which may consist of single or multiple fields, and when multiple fields are used as a primary key, then it is known as composite keys.

If the table has a primary key defined in any of the fields, then it cannot have two or more records having the same values.

#sql #sql primary key #primary key