MySQL Function for Calculating the Working Days between 2 Dates

Lately I needed a MySQL stored function to calculate the working days (or business days) between 2 dates, however all the solutions I found online were either not configurable in terms of which week days count as working days, or really hard to read/understand. So I rolled my own, and decided to post it here in case anyone else finds it useful.

Here’s the function declaration code, as well as a usage example, hosted in GitHub (or you can find it in if it’s not showing in your browser):

The function accepts 2 dates, as well as a string that specifies which week days should count as working days. The week days are input as the integers corresponding to their WEEKDAY function representation, i.e.:

0 = Monday
1 = Tuesday
2 = Wednesday
3 = Thursday
4 = Friday
5 = Saturday
6 = Sunday

Thus if the working days are Monday to Friday, the workdays argument would be ‘01234’, and if for a more abstact example the working days are Tuesday to Thursday plus Saturday, the workdays argument would then become ‘1235’.

The function itself determines the start and end dates from the first 2 arguments (so you can use it with the earlier and later dates in any position), counts the number of whole weeks (Monday to Sunday) between the 2 dates, and then loops through the remaining days not belonging to a whole week and counts them if they are contained in the 3rd argument.

Hope you found it useful!

Display Custom Equation Numbers in Wolfram Mathematica

If you would like to use the EquationNumbered style for typesetting, but using your own equation numbers or designations instead of the automatically generated ones, you can simply edit the cell expression by going into the menu Cell > Show Expression. If you do this on a blank EquationNumbered cell, you should get code like the following:

Cell[BoxData[ FormBox["", TraditionalForm]], "EquationNumbered"]

There, you need to override the CellFrameLabels option of the parent Cell, with the following code:

{{None, Cell[ TextData[{"(YOUR_DESIGNATION_HERE)"}], "EquationNumbered"]}, {None, None}}

Substitute the YOUR_DESIGNATION_HERE text with the number or designation you want to assign to your equation. For example if you want to call it A1, your cell should end up like this:

Cell[BoxData[ FormBox["", TraditionalForm]], "EquationNumbered", CellFrameLabels->{{None, Cell[ TextData[{"(A1)"}], "EquationNumbered"]}, {None, None}}]

Now you can disable the menu Cell > Show Expression option, and your cell is ready for you to type your equation in!

Laplace's equation in polar coordinates

Clear the Field of an non-Editable AngularUI Typeahead

When working with non-editable AngularUI Typeaheads (i.e. ones that have the typeahead-editable attribute set to false), a logical thing to do would be to erase the typeahead input field’s view value if the user doesn’t select a valid typeahead option. However, there’s no built-in option to do just that, so here’s a workaround.

The main idea here is to use the ng-blur attribute to set a function that will clear the typeahead field if no valid option was selected. To do that first we need to access by name the form controller object containing the typeahead. If the typeahead is not contained in a form element, what we can do is declare one of its parent elements as a form controller using ng-form, and give names to both of them:

<div ng-form name="myForm"> <input type="text" name="myField" ng-model="myField" ng-blur="clearUnselected()" typeahead="myField in myFields" typeahead-editable="false" /> </div>

Now we can access the the typeahead’s form properties from the AngularJS controller, and reset its $viewValue property if no valid option was selected by the user. We wrap this into an AngularJS $timeout because there’s a delay between clicking on an option and the corresponding model updating. Don’t forget to inject the $timeout service into your controller!

//inside your controller $scope.clearUnselected = function () { $timeout(function () { if (!$scope.myField) { //the model was not set by the typeahead $scope.myForm.myField.$setViewValue(''); $scope.myForm.myField.$render(); } }, 250); //a 250 ms delay should be safe enough }

PrestaShop Module Development by Fabien Serny – a book review

This book, written by one of the original members of the Prestashop developer team, is an invaluable resource for anyone whose income depends at least in part on developing Prestashop modules. The time savings alone, as compared to having to browse through the Prestashop classes and native modules just to find how an example of functionality similar to what you require, are definitely worth the price of admission.

The book outlines Prestashop best practices, goes into detail on the different types of modules, and describes the usage of helper form and list classes, the context object, overrides, and how to handle module updates. Part of this information can be also found in Prestashop’s developer guide, however the book goes into much more detail and lays out quite explanatory code samples. However, the most useful part of it all might be the Native Hooks Appendix, which has a list of all the 145 native hooks (as of Prestashop 1.6) with their descriptions, parameters, and the files they are called from.

As for stuff missing from the book, I believe a section on Functional Testing of modules would have been really useful, since the Prestashop developer community would surely benefit from incorporating automated testing into its development standards. Apart from this, the book’s a real time saver if you’re a Prestashop beginner, and even if you’ve got quite a few modules under your belt, it should at least help to improve the quality of your code.

Get data from a Jet DB (Microsoft Access) file in Windows using LibreOffice

If you need to access data from a Jet DB file, there’s a relatively simple way to do it in Windows without Microsoft Office, by using LibreOffice and creating an ODBC data source.

First open your Windows/SysWOW64/ folder in explorer and run odbcad32.exe as Administrator. The ODBC Data Source Administrator should open. Once it does, stay on the User DSN tab and click the Add button. Select the Microsoft Access Driver and click Finish. On the new window that will open write the name of your file (or anything you want, for that matter) in the Data Source Name field, next click on the Select button of the Database subsection, and select your file. Click OK to close both windows.

Now that the data source is set up, open Libre Office Base, select Connect to an existing database, and select ODBC in the dropdown menu. Click on Browse, choose the data source you just created, and click OK. Click on Finish and save your config as a new file. Now you should have access to all of the database tables in the file.

This method has the disadvantage of requiring you to create a new ODBC data source for each file you need to open, but it sure beats all other ways I’ve found so far that don’t require using a suitable version of Microsoft Access.

How to fix blank screen in Preferences > Themes on the Prestashop Back Office

The Symptoms

You’ve linked your shop to your Prestashop Addons account, where you’ve previously or recently bought a theme. You try opening the Preferences > Themes menu, just to find that after trying to load the page for a while, you either get a blank page (even with dev mode on) or a cryptic 500 error.

The cause

When the Admin Themes Controller initializes, it checks if you’re logged into Prestashop Addons, and if so, whether there’s a theme in your account that hasn’t been installed in your store. If there is, it tries to download it automatically, and here’s where the problem lies: your server is timing out during this connection. If you go to your server error log, you’ll probably find an error such as mod_fcgid: read data timeout in xx seconds if your PHP installation is running on FastCGI.

The Solution

Unfortunately, if you are running on a shared host you almost certainly won’t have the required access necessary to change the server’s timeout parameters. In that case the only course of action is to disable the theme auto-download functionality in AdminThemesController.php, and this can be cleanly done in an override. This is all the code you need in your override:

class AdminThemesController extends AdminThemesControllerCore
    public function init()
        $this->logged_on_addons = false;

If you don’t know how to create overrides don’t worry, you can download the following zip with the override already in place. All you need to do is extract the folder within, upload it into your store’s root Prestashop folder, and delete the file cache/class_index.php on your store so the override is detected.