Embedded Resource Property Generator

The Embedded Resource Property Generator is a Source Generator which generates properties for text file embedded resources in a project, in a similar way to how properties are generated from the string resources in .resx files.

By adding the [EmbeddedResourceProperties] attribute to a partial class, and specifying the filename extension and folder path to search, the source generator will add a property to the class for each matching embedded resource file. Accessing the property will return the text content of the embedded resource file.

Why not just use a resx file?

The use case for this project is when you have a large number of text files that you want to embed in your project, such as SQL queries, and you wish to develop these files with an external editor that supports syntax highlighting, execution, debugging, and other features.

While resx files do support including files, doing so requires either the use of another custom editor, or manipulating the xml of the resx file directly.

What's wrong with just using Assembly.GetManifestResourceStream?

The purpose of providing properties to access the text, is to aid the developer by generating doc-comments for the properties, showing the first few lines of the file.

/// <summary>Text value of the Embedded Resource: GoodIndenting.cypher</summary>
/// <value>
/// <code>
/// MERGE (n)
///   ON CREATE SET n.prop = 0
/// MERGE (a:A)-[:T]-(b:B)
///   ON CREATE SET a.name = 'me'
///   ON MATCH SET b.name = 'you'
/// RETURN a.prop
/// </code>
/// </value>
/// <remarks>
/// The value is read from the embedded resource on first access.
/// </remarks>
public static string GoodIndenting => 
  // Generated code to read the resource "Namespace.ClassName.GoodIndenting.cypher";

The full names of the embedded resources are also generated, and no longer need to be supplied by the developer, making it easy to move the location of the resource files to another directory, without needing to find and fix all the references to the resource names.

Usage

1. Add a reference to the EmbeddedResourcePropertyGenerator project.
2. Add the following section to your .csproj file, to include all EmbeddedResource files as Additional Files for the source generators:

     <PropertyGroup>
       <AdditionalFileItemNames>$(AdditionalFileItemNames);EmbeddedResource</AdditionalFileItemNames>
     </PropertyGroup>

3. Add a directory to your project to group the files you want to embed.
4. Add text files to your project, in that directory, and set their Build Action to EmbeddedResource.

   > SqlQueries
       SelectAll.sql
       SelectById.sql
   Program.cs
   

     <ItemGroup>
       <EmbeddedResource Include="SqlQueries\SelectAll.sql" />
       <EmbeddedResource Include="SqlQueries\SelectById.sql"/>
     </ItemGroup>

5. Add a partial class to your code.
6. Include a using statement to the namespace of the code generator.
7. Put the attribute [EmbeddedResourcePropertyGenerator] on the class.
8. Specify the extension and folder path to search for embedded resources.
9. Use the properties generated on the partial class.

   using Datacute.EmbeddedResourcePropertyGenerator;
   
   [EmbeddedResourceProperties(".sql", "SqlQueries")]
   public static partial class SqlQuery;
   
   class Program
   {
       static void Main()
       {
           Console.WriteLine(SqlQuery.SelectAll);
       }
   }

Localisation and External Overrides

Localisation and External Overrides are not supported. If you need these features, consider using a resx file instead.

Non-text File Types

This project expects text files so that it can generate properties that are strings. It currently expects UTF-8 encoded files.

If you need to embed other types of files, use the Assembly.GetManifestResourceStream method directly.

Extending the Behaviour

The generated code includes a private nested class EmbeddedResource containing:

Method or Class	Purpose
Read(string resourceName)	Method for reading embedded resources
BackingField	Nested class caching the property values
ResourceName	Nested class holding the resource names

The implementation supports including two partial methods that can be implemented in the same partial class as the generated properties.

If the partial methods are not implemented, the calls to them are removed, and the code effectively reduces to:

public static string Example =>
        EmbeddedResource.BackingField.Example ??= EmbeddedResource.Read(EmbeddedResource.ResourceName.Example);

Partial methods:

• ReadEmbeddedResourceValue - This method is called to allow the class to override how the value representing the content of the embedded resource is obtained. If the backingField parameter is null when this method ends, the default implementation will be used.
• AlterEmbeddedResourceReturnValue - This method is called after the text content has been read, and can be used to modify the text content before it is returned. Altering the returned value does not affect the value stored in the backing field.

    [EmbeddedResourceProperties(".sql", "SqlQueries")]
    public static partial class SqlQuery
    {
        static partial void ReadEmbeddedResourceValue(
            ref string? backingField, 
            string resourceName, 
            string propertyName)
        {
            // This method is called before the default implementation.

            // The default implementation only reads the resource
            // if the backingField is null, so by setting it in this method,
            // the default implementation can be bypassed.

            // The backingField is a reference to a static field
            // for the property, and will be null for the first call,
            // but will retain the value for subsequent calls
            // for the same property.

            // Use custom logic to read the text content given the names
            // of the resource, and of the property.
            backingField ??= CustomReader(resourceName, propertyName);
        }

        static partial void AlterEmbeddedResourceReturnValue(
            ref string value,
            string resourceName,
            string propertyName);
        {
            // The value parameter is a reference to a variable that 
            // will be returned as the value of the property.
            
            // Implement custom logic to alter the value.
            value = CustomValueAlteringMethod(value, resourceName, propertyName);
        }
    }

This is an example of the code generated for a property, showing how the partial methods are called:

/// <summary>Text value of the Embedded Resource: Example.txt</summary>
/// <value>
/// <code>
/// This is the content of the Example.txt file.
/// Only the first few lines are shown here.
/// </code>
/// </value>
/// <remarks>
/// The value is read from the embedded resource on first access.
/// </remarks>
public static string Example
{
    get
    {
        ReadEmbeddedResourceValue(ref EmbeddedResource.BackingField.Example, EmbeddedResource.ResourceName.Example, "Example");
        var value = EmbeddedResource.BackingField.Example ??= EmbeddedResource.Read(EmbeddedResource.ResourceName.Example);
        AlterEmbeddedResourceReturnValue(ref value, EmbeddedResource.ResourceName.Example, "Example");
        return value;
    }
}

Thanks

Thanks to Andrew Lock for his Series: Creating a source generator.

Future Enhancements

• Add an option to leave out the Read method.
  • It is now included in the generated code for each class, but an implementation of the ReadEmbeddedResourceValue partial method might make it unnecessary.
• Support for alternative text encodings.
  • Overriding ReadEmbeddedResourceValue is a technique that can be used to read the text content of the embedded resource with a different encoding, but the doc-comment will still be generated expecting UTF-8.
• Support for specifying the number of lines to include in the doc-comment (including zero to exclude the code section).
  • This is currently set to 10 lines.
• Support generating text formatting methods.
  • Call CompositeFormat.Parse on the loaded text, and additionally count the number of format items, and generate a method that takes the same number of arguments.
  • Using a resx file is probably a better fit that adding this feature.
• Support generating ReadOnlySpan<byte> properties instead of string
  • The decoding from utf-8 may not be needed.