Added 'if_null` filter for Liquid tags.

src/Extensions/Filters/MIISLiquidFilters/IfNullFilter.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Linq;
+using System.Collections;
+
+namespace MIISHandler.Filters
+{
+
+    //Needed by MIIS to add the correct reference to DotLiquid
+    public class IfNullFilterFactory : IFilterFactory
+    {
+        Type IFilterFactory.GetFilterType()
+        {
+            return typeof(IfNullFilter);
+        }
+    }
+
+    public static class IfNullFilter
+    {
+        /// <summary>
+        /// This filter returns the value if it's not null, or the parameter if the value to filter it's null
+        /// Very useful to use default values. It can be used several times in the same tag, and saves lots of if-else-end Liquid tags
+        /// </summary>
+        /// <param name="input">Any parameter</param>
+        public static object IfNull(object input, object defValue)
+        {
+            return input ?? defValue;
+        }
+    }
+}

src/Extensions/Filters/MIISLiquidFilters/MIISLiquidFilters.csproj

@@ -42,6 +42,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="IfNullFilter.cs" />
     <Compile Include="UrlFilters.cs" />
     <Compile Include="ReverseFilter.cs" />
     <Compile Include="ConcatFilter.cs" />

src/Extensions/Filters/MIISLiquidFilters/Properties/AssemblyInfo.cs

@@ -32,5 +32,5 @@
 // You can specify all the values or you can default the Build and Revision Numbers
 // by using the '*' as shown below:
 // [assembly: AssemblyVersion("1.0.*")]
-[assembly: AssemblyVersion("1.0.0.0")]
-[assembly: AssemblyFileVersion("1.0.0.0")]
+[assembly: AssemblyVersion("1.1.0.0")]
+[assembly: AssemblyFileVersion("1.1.0.0")]

src/MIISHandler/Properties/AssemblyInfo.cs

@@ -31,5 +31,5 @@
 //
 // You can specify all the values or you can default the Revision and Build Numbers 
 // by using the '*' as shown below:
-[assembly: AssemblyVersion("3.1.0")]
-[assembly: AssemblyFileVersion("3.1.0")]
+[assembly: AssemblyVersion("3.2.0")]
+[assembly: AssemblyFileVersion("3.2.0")]

src/Tests/Tests.csproj

@@ -182,6 +182,7 @@
     <Content Include="insertfiles\mixed_md_html.md" />
     <Content Include="insertfiles\component01.md" />
     <Content Include="insertfiles\inheritance.md" />
+    <Content Include="if-null-filter.md" />
     <None Include="Web.Debug.config">
       <DependentUpon>Web.config</DependentUpon>
     </None>

src/Tests/Web.config

@@ -5,9 +5,9 @@
     <add key="MIIS:Lang" value="!!DataFromFile ~/_data/langs/en.yml"/>
     <add key="MIIS:Logo" value="images/logo.png"/>
     <add key="MIIS:Description" value="Default description"/>
-    <add key="MIIS:Caching" value="0"/><!-- No Caching: Useful for debugging -->
+    <add key="MIIS:Caching" value="false"/><!-- No Caching: Useful for debugging -->
     <add key="MIIS:EnableMDExtensions" value="hardlinebreak+bootstrap+smartypants"/>
-    <add key="copyright" value="JM Alarcón 2017-2019"/>
+    <add key="copyright" value="JM Alarcón 2017-2020"/>
     <add key="cssfile" value="~/CSS/github.css"/>
     <add key="MIIS:TemplateName" value="readthedocs"/>
     <add key="MIIS:Layout" value="main.html"/>

src/Tests/if-null-filter.md

@@ -0,0 +1,62 @@
+---
+Title: 'if_null' liquid filter usage
+#image: /images/myImage.png
+#og-image: /images/myOGImage.png
+bg-image: /images/myBGImage.png
+---
+
+# 'if_null' filter usage
+
+MIIS adds in 3.2.0 a custom filter called `if_null`. This filter allows you to save if-else-end Liquida tags and make your templates much more concise and readable.
+
+For example, imagine that you have 3 possible images that you can use in a page:
+
+- `image`: the normal if_null field used for blog posts or any other file.
+- `bg-image`: a background image that your template design optionally can use as an specific image for the header's background.
+- `og-image`: a specific image to be used for social sharing in the Open Graph headers for the page
+
+In the social headers code you want to make the precedence of this images this way: 
+
+`og-image > image > bg-image`
+
+So, if `og-image` is not available, use `image` and if `image` is not available either, then use `bg-image`.
+
+In normal Liquid syntax you would probably do something like this:
+
+```liquid
+{%- raw -%}
+{%- if og-image -%}
+
+{%- capture imgurl -%}{{ og-image | absolute_url }}{%- endcapture -%}
+
+{%-elsif image -%}
+
+{%- capture imgurl -%}{{ image | absolute_url }}{%- endcapture -%}
+
+{%-else bg-image -%}
+
+{%- capture imgurl -%}{{ bg-image | absolute_url }}{%- endcapture -%}
+
+{%- endif -%}
+
+<meta property="og:image" content="{{ imgurl }}" />
+{%- endraw -%}
+```
+
+>Note: Thanks to MIIS' `absolute_url` filter you save some "ifs" inside the capture taking into account if it's an absolute, relative or relative to the root URL.
+
+Well, with the `if_null` filter, you can now simple write:
+
+```liquid
+{%- raw - %}
+<meta property="og:image" content="{{ og-image | if_null: image | if_null: bg-image | absolute_url }}" />
+{%- endraw -%}
+```
+
+and you're done! Much clearer and succint.
+
+You can check it in use in the code for this page. Note that this page has only defined the `bg-image` parameter, therefore in the next paragraph you should see the URL for that image:
+
+`{{ og-image | if_null: image | if_null: bg-image | absolute_url }}`
+
+You can play with it uncommenting the other images in the Front-Matter and see how it behaves.

src/Tests/toc.md

@@ -17,6 +17,7 @@ _{{customfield}}_
 - [Liquid Syntax in HTML](~/liquid.mdh){target="_blank"}
 - [Raw content (text/plain) from MDH](~/raw.mdh){target="_blank"}
 - [Custom filters](~/customfilters.md)
+- [if_null MIIS filter](~/if-null-filter.md)
 - [Custom tags](~/customtags.md)
 - [Custom Front-Matter and Request params](~/customFMSrc.md?param1=1&s=Hi)
 - [Post list - FileFromFolder custom FMSource](~/posts/)