Enhance documentation and introduce IReadQuery interface

Updated XML documentation in ConfigurationExtension.cs for better clarity.
Removed the old implementation and retained the functionality of GetOrDefault<T>.

Introduced a new IReadQuery<TEntity> interface in IReadQuery.cs,
providing methods for both asynchronous and synchronous entity queries,
along with comprehensive documentation for each method.

DigitalData.Core.Abstractions/ConfigurationExtension.cs

@@ -1,30 +1,29 @@
 using Microsoft.Extensions.Configuration;
 
-namespace DigitalData.Core.Abstractions
+namespace DigitalData.Core.Abstractions;
+
+/// <summary>
+/// Extension methods for the <see cref="IConfiguration"/> interface, providing 
+/// additional functionality for retrieving configuration values with default behavior.
+/// </summary>
+public static class ConfigurationExtension
 {
     /// <summary>
-    /// Extension methods for the <see cref="IConfiguration"/> interface, providing 
+    /// Retrieves a configuration value for the specified key, or returns a default value 
-    /// additional functionality for retrieving configuration values with default behavior.
+    /// of type <typeparamref name="T"/> if the configuration is not found or the key is null.
     /// </summary>
-    public static class ConfigurationExtension
+    /// <typeparam name="T">The type of the object to retrieve from the configuration.</typeparam>
-    {
+    /// <param name="configuration">The <see cref="IConfiguration"/> instance.</param>
-        /// <summary>
+    /// <param name="key">The optional key to look for in the configuration. If null, the method 
-        /// Retrieves a configuration value for the specified key, or returns a default value 
+    /// retrieves the root configuration.</param>
-        /// of type <typeparamref name="T"/> if the configuration is not found or the key is null.
+    /// <returns>
-        /// </summary>
+    /// An instance of <typeparamref name="T"/> populated from the configuration values, or 
-        /// <typeparam name="T">The type of the object to retrieve from the configuration.</typeparam>
+    /// a new instance of <typeparamref name="T"/> if no matching configuration is found.
-        /// <param name="configuration">The <see cref="IConfiguration"/> instance.</param>
+    /// </returns>
-        /// <param name="key">The optional key to look for in the configuration. If null, the method 
+    public static T GetOrDefault<T>(this IConfiguration configuration, string? key = null)
-        /// retrieves the root configuration.</param>
+        where T : new()
-        /// <returns>
+        => (key is null
-        /// An instance of <typeparamref name="T"/> populated from the configuration values, or 
+            ? configuration.Get<T>()
-        /// a new instance of <typeparamref name="T"/> if no matching configuration is found.
+            : configuration.GetSection(key).Get<T>())
-        /// </returns>
+        ?? new T();
-        public static T GetOrDefault<T>(this IConfiguration configuration, string? key = null)
-            where T : new()
-            => (key is null
-                ? configuration.Get<T>()
-                : configuration.GetSection(key).Get<T>())
-            ?? new T();
-    }
 }

DigitalData.Core.Application/Interfaces/Repository/IReadQuery.cs

@@ -0,0 +1,80 @@
+using System.Linq.Expressions;
+
+namespace DigitalData.Core.Application.Interfaces.Repository;
+
+/// <summary>
+/// Provides methods for executing common queries on a given entity type.
+/// This interface abstracts away the direct usage of ORM libraries (such as Entity Framework) for querying data
+/// and provides asynchronous and synchronous operations for querying a collection or single entity.
+/// </summary>
+/// <typeparam name="TEntity">The type of the entity being queried.</typeparam>
+public interface IReadQuery<TEntity>
+{
+    /// <summary>
+    /// Adds a filter to the query using the specified predicate expression.
+    /// This method allows chaining multiple filter conditions to refine the query results.
+    /// </summary>
+    /// <param name="expression">An expression that defines the filter condition for the entity.</param>
+    /// <returns>The current <see cref="IReadQuery{TEntity}"/> instance with the applied filter.</returns>
+    public IReadQuery<TEntity> Where(Expression<Func<TEntity, bool>> expression);
+
+    /// <summary>
+    /// Asynchronously retrieves the first entity or a default value if no entity is found.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation. The task result contains the entity or a default value.</returns>
+    public Task<TEntity?> FirstOrDefaultAsync();
+
+    /// <summary>
+    /// Asynchronously retrieves a single entity or a default value if no entity is found.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation. The task result contains the entity or a default value.</returns>
+    public Task<TEntity?> SingleOrDefaultAsync();
+
+    /// <summary>
+    /// Asynchronously retrieves a list of entities.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation. The task result contains the list of entities.</returns>
+    public Task<IEnumerable<TEntity>> ToListAsync();
+
+    /// <summary>
+    /// Asynchronously retrieves the first entity. Throws an exception if no entity is found.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation. The task result contains the first entity.</returns>
+    public Task<TEntity> FirstAsync();
+
+    /// <summary>
+    /// Asynchronously retrieves a single entity. Throws an exception if no entity is found.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation. The task result contains the single entity.</returns>
+    public Task<TEntity> SingleAsync();
+
+    /// <summary>
+    /// Synchronously retrieves the first entity or a default value if no entity is found.
+    /// </summary>
+    /// <returns>The first entity or a default value.</returns>
+    public TEntity? FirstOrDefault();
+
+    /// <summary>
+    /// Synchronously retrieves a single entity or a default value if no entity is found.
+    /// </summary>
+    /// <returns>The single entity or a default value.</returns>
+    public TEntity? SingleOrDefault();
+
+    /// <summary>
+    /// Synchronously retrieves a list of entities.
+    /// </summary>
+    /// <returns>The list of entities.</returns>
+    public IEnumerable<TEntity> ToList();
+
+    /// <summary>
+    /// Synchronously retrieves the first entity. Throws an exception if no entity is found.
+    /// </summary>
+    /// <returns>The first entity.</returns>
+    public TEntity First();
+
+    /// <summary>
+    /// Synchronously retrieves a single entity. Throws an exception if no entity is found.
+    /// </summary>
+    /// <returns>The single entity.</returns>
+    public TEntity Single();
+}