Partial class, with overrrides for the various overloads of DbContext.SaveChanges, for getting the inner exceptions from a "DbEntityValidationException" event. Change "DataModel" to the name you gave your data model.

DbContextExtensions.cs

public partial class DataModel
{
	public override int SaveChanges()
	{
		try
		{
			return base.SaveChanges();
		}
		catch (DbEntityValidationException ex)
		{
			string exceptionMessage = GenerateVerboseExceptionMessage(ex);

			// Throw a new DbEntityValidationException with the improved exception message.
			throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors, ex.InnerException);
		}
	}

	public override Task<int> SaveChangesAsync()
	{
		try
		{
			return base.SaveChangesAsync();
		}
		catch (DbEntityValidationException ex)
		{
			string exceptionMessage = GenerateVerboseExceptionMessage(ex);

			// Throw a new DbEntityValidationException with the improved exception message.
			throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors, ex.InnerException);
		}
	}

	public override Task<int> SaveChangesAsync(CancellationToken cancellationToken)
	{
		try
		{
			return base.SaveChangesAsync(cancellationToken);
		}
		catch (DbEntityValidationException ex)
		{
			string exceptionMessage = GenerateVerboseExceptionMessage(ex);

			// Throw a new DbEntityValidationException with the improved exception message.
			throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors, ex.InnerException);
		}
	}


	private string GenerateVerboseExceptionMessage(DbEntityValidationException ex)
	{
		var errorMessages = new List<string>();
		foreach (var validationResult in ex.EntityValidationErrors)
		{
			string entityName = validationResult.Entry.Entity.GetType().Name;
			foreach (var error in validationResult.ValidationErrors)
			{
				errorMessages.Add(entityName + "." + error.PropertyName + ": " + error.ErrorMessage);
			}
		}

		// Join the list to a single string.
		var fullErrorMessage = string.Join(Environment.NewLine, errorMessages);

		return string.Concat(ex.Message, " The validation errors are: ", Environment.NewLine, fullErrorMessage);
	}
}