Add messages to obsolete specs for clarity (#373)

* Add messages to obsolete specs for clarity

* Update messages to be more straightforward & concise

Author: Rowe2ryWA

Specification.EntityFramework6/src/Ardalis.Specification.EntityFramework6/RepositoryBaseOfT.cs

@@ -102,14 +102,14 @@ public virtual async Task<T> GetByIdAsync<TId>(TId id, CancellationToken cancell
     }
 
     /// <inheritdoc/>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     public virtual async Task<T> GetBySpecAsync(ISpecification<T> specification, CancellationToken cancellationToken = default)
     {
         return await ApplySpecification(specification).FirstOrDefaultAsync(cancellationToken);
     }
 
     /// <inheritdoc/>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     public virtual async Task<TResult> GetBySpecAsync<TResult>(ISpecification<T, TResult> specification, CancellationToken cancellationToken = default)
     {
         return await ApplySpecification(specification).FirstOrDefaultAsync(cancellationToken);

Specification.EntityFrameworkCore/src/Ardalis.Specification.EntityFrameworkCore/RepositoryBaseOfT.cs

@@ -94,14 +94,14 @@ public virtual async Task<int> SaveChangesAsync(CancellationToken cancellationTo
     }
 
     /// <inheritdoc/>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     public virtual async Task<T?> GetBySpecAsync(ISpecification<T> specification, CancellationToken cancellationToken = default)
     {
         return await ApplySpecification(specification).FirstOrDefaultAsync(cancellationToken);
     }
 
     /// <inheritdoc/>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     public virtual async Task<TResult?> GetBySpecAsync<TResult>(ISpecification<T, TResult> specification, CancellationToken cancellationToken = default)
     {
         return await ApplySpecification(specification).FirstOrDefaultAsync(cancellationToken);

Specification/src/Ardalis.Specification/IReadRepositoryBase.cs

@@ -34,7 +34,7 @@ public interface IReadRepositoryBase<T> where T : class
     /// A task that represents the asynchronous operation.
     /// The task result contains the <typeparamref name="T" />, or <see langword="null"/>.
     /// </returns>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     Task<T?> GetBySpecAsync(ISpecification<T> specification, CancellationToken cancellationToken = default);
 
     /// <summary>
@@ -46,7 +46,7 @@ public interface IReadRepositoryBase<T> where T : class
     /// A task that represents the asynchronous operation.
     /// The task result contains the <typeparamref name="TResult" />.
     /// </returns>
-    [Obsolete]
+    [Obsolete("Use FirstOrDefaultAsync<T> or SingleOrDefaultAsync<T> instead. The SingleOrDefaultAsync<T> can be applied only to SingleResultSpecification<T> specifications.")]
     Task<TResult?> GetBySpecAsync<TResult>(ISpecification<T, TResult> specification, CancellationToken cancellationToken = default);
 
     /// <summary>