Eager vs Lazy Loading - Overview - Part 1 is a free tutorial by Chad Darby from Spring Framework course
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English
-: In this video, we're gonna cover fetch types for eager versus lazy. Now, when we load data, or we retrieve or fetch data, the question is should we retrieve everything? So, an eager load will pull in everything. Lazy load will retrieve data only on request. So, imagine we have an instructor. An instructor has a list of courses. Depending on the loading type, that will determine when and how the data is loaded from the data base by Hibernate. And, it'll also has an implication on your actual performance of your given app. Now, with eager loading, it will actually load all your dependent entities. So, it'll load the instructor and and all of their courses at once. So, it will do a one, quick shot to the database, grab all the data and bring it back. Now, this may not be a big deal if you only have a small number instructor and a small number of courses, but you can imagine if you had a lot of data out there, that could actually impact the performance of your application. Now, let's take a look at another example with eager loading. So, what about a course and students? So, this could easily turn into a performance nightmare. So, if we were to load a course and then actually load all of the students for the course, then this could possibly slow down our application or not even possibly most likely, it will slow down our application. Because, just like the course you are attending now, a given course could have 10,000, 20,000, maybe 50,000 students and we really don't need all that data at this point. So, in our app, if we're simply searching for a course by keyword, like just doing your normal search there, we only want a list of matching courses. But eager loading, it will still load all the students for each course and that's not good, right? We only want the titles or the descriptions of the courses but not all of the students. So, the best practice ... ding, ding, ding! The best practice in the industry is to only load data when absolutely needed. So, you should prefer lazy loading instead of eager loading. Now, there's always exceptions to the rule, right? And there's also special use cases, but in general, the recommendation is to prefer lazy loading over eager loading. Alrighty, so with lazy loading. So, lazy loading will load the main entity first, and then it will actually load the dependent entities on demand, at a later time. So, here we have a course, so it will actually load the course first and then, when you need a list of students, then that's when it will actually go to the database and load those students on demand. So, they will be loaded at a later time. And, again, remember, the preference here is on making use of lazy loading to make sure our application performs in a fast manner. So, lazy loading is preferred.
Eager vs Lazy Loading - Overview - Part 1 Spring 5: Learn Spring 5 Core, AOP, Spring MVC, Spring Security, Spring REST, Spring Boot 2, Thymeleaf, JPA & Hibernate

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