Jing Zhang

Jing Zhang

1592018361

When Does JPA Set the Primary Key

Learn about the different strategies JPA uses to generate the primary key for an entity and at which moment each strategy sets the key value during persistence.

1. Overview

In this tutorial, we’ll illustrate the moment when JPA assigns a value to the primary key. We’ll clarify what the JPA specification says, and then, we’ll show examples using various JPA strategies for primary key generation.

2. Problem Statement

As we know, JPA (Java Persistence API) uses the EntityManager to manage the lifecycle of an Entity. At some point, the JPA provider needs to assign acvalue to the primary key. So, we may find ourselves asking, when does this happen? And where is the documentation that states this?

The JPA specification says:

A new entity instance becomes both managed and persistent by invoking the persist method on it or by cascading the persist operation.

So, we’ll focus on the EntityManager.persist() method in this article.

#jpa #java #developer

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When Does JPA Set the Primary Key
Jerod  Mante

Jerod Mante

1601994240

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

Jing Zhang

Jing Zhang

1592018361

When Does JPA Set the Primary Key

Learn about the different strategies JPA uses to generate the primary key for an entity and at which moment each strategy sets the key value during persistence.

1. Overview

In this tutorial, we’ll illustrate the moment when JPA assigns a value to the primary key. We’ll clarify what the JPA specification says, and then, we’ll show examples using various JPA strategies for primary key generation.

2. Problem Statement

As we know, JPA (Java Persistence API) uses the EntityManager to manage the lifecycle of an Entity. At some point, the JPA provider needs to assign acvalue to the primary key. So, we may find ourselves asking, when does this happen? And where is the documentation that states this?

The JPA specification says:

A new entity instance becomes both managed and persistent by invoking the persist method on it or by cascading the persist operation.

So, we’ll focus on the EntityManager.persist() method in this article.

#jpa #java #developer

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

Things To Know Before Playing A Chess Game

If you love the clash of titans or other thrilling games, a chess game can resemble you all. You can take part in a chess game as per your interest without even waiting for the consent of anyone. Not only it can augment your ability of taking decisions but it will also boost your overall development. Playing chess incorporates loads of benefits however you should still keep a few things in mind before taking part in your favorite chess game.

It can enable a mix of brilliance and intelligence

Playing chess can increase your ability of mind by forcing it to think a lot. From building a huge concentration to augmented intelligence, you can get all by only taking part in your beloved chess game with the help of antique chess sets for sale in the market. It is a game that can be played inside your home or office, and you can also consider it playing without one partner. If you don’t have anyone available to play with you, computer and mobile devices might be your favorite companion.

Does playing chess can make you crazy?

Those who take part in mental games like chess face a higher level of mental exhaustion. It is true but we can’t say it craziness. If you find it crazy about these chess games then it would be most probably before the game. This game can consume lots of minds, and it will require lots of whereabouts that will help you do well in the game without facing further defeats.

It can enable different cognitive benefits

The games like chess require lots of mental balance and huge freeness of mind so that you can think a lot when going ahead with any move at a chess set in wooden box. It is a silent war zone with no blood where you need to keep your eye on the moves of the opponent and to play accordingly to do well in the game. By playing your favorite chess game, you can also experience different cognitive benefits without facing any frills in your everyday life.

#chess set in wooden box #chess set #wooden chess set #antique chess sets for sale

Nandini roy

Nandini roy

1626279136

Blogger Advanced SEO Settings for beginners

Without proper SEO it will take more time to rank your blog posts and drive organic traffic from Google Search Results. If you have started a blog on Google Blogger and want to enable Blogger Advanced SEO settings, then stay with me till the end of this guide.

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#blogger #advanced #seo settings #blogger advanced seo settings #blogger advanced settings