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    <ul> <li><p>The factory should <em>only</em> care about creating entities. I personally preferr to put validation both in my views and in the model layer. I'd use some library like jQuery's validation plugin to make some <strong>essential</strong> validation on the client side (like checking if required fields have data). And then do the "hardcore" validation on the model. I do this is by using a simple BaseEntity abstract class which all entities extend, and since you asked for an example, here it is: </p> <pre><code>abstract class BaseEntity { public function isValid(); } class MyEntity extends BaseEntity { public function isValid() { //actual validation goes here } } </code></pre> <p>You could also make use of a static helper class with some basic validation methods:</p> <pre><code>class ValidationHelper { public static function isValidPhonenumber($value) { //check valid phonenumber, using a regex maybe } public static function isAlphanumeric($value) { //check for letters and numbers only } } </code></pre> <p>Many argue against static methods because they can break unit tests, but in this case they are pretty basic and they don't have external dependencies, thus making them "safer".</p></li> <li><p>When it comes to checking for already existing entities you can do this by querying your DB to see if the entity is already there before adding/updating, or (this is how I like to do it) you could add a <code>unique</code> index to those columns that can't be repeated in the DB, and then wrap the create or update queries in a try-catch block (the query will throw a unique constraint violation, if two users have same e-mail for example) and then show the proper error message</p></li> <li><p>On your last question it comes down to a matter of preference. If your DB will get a million hits in 1 minute, then it's probably better to use lazy loading to avoid fetching unnecesary data until it's needed. But if your database is relatively small you could perfectly use eager loading without sacrificing too much performance. Again, this is a matter of personal preference.</p></li> </ul> <p>hope some of this rambling makes sense, cheers!</p>
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    1. COThanks for your comment! A) I'm not sure about putting validation in the entity. Would you consider validating captcha be part of the business logic? And what if I have admin panel to manually add users without the need of captcha? B) Yes I can, but the question is whose responsibility it is? Validation layer? Factory? Repository? C) Ok but what if I have User who have posts that have comments, will it be smart to load all this data to display the user profile page?
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      1. USDmitry Kudryavtsev
    2. COa) it depends on your needs really, i have found it "easier" to have validation in the entity itself using helper classes. but adding an extra layer of validation is perfectly fine. b) i would say it's the validation's layer responsibility. if two Accounts can't have the same number and you try to add one with a number that already exists, that means that entity is **invalid**, or at least thats what i think.
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    3. COc) this also depends on what you want. if you are going to show all that info at once on the profile page then yes, load all the info in one call. but if you show, lets say, only the posts, and when you click on one you show the comments, it would be better to load the comments in that moment, maybe using ajax
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