Dapper and the NVARCHAR(4000) arguments - http://diegogiacomelli.com.br/dapper-and-the-nvarchar-4000-arguments

dapper.sample1.cs

conn.Execute(
  "UPDATE Contact SET Date = @date, Info = @info WHERE ExternalId = @externalId", 
  new
  {
      Date = DateTime.UtcNow,
      info = new DbString { Value = info, Length = 500, IsAnsi = false, IsFixedLength = false },
      externalId = new DbString { Value = externalId, Length = 100, IsAnsi = true, IsFixedLength = false }      
  });

dapper.sample2.cs

 conn.Execute(
  "UPDATE Contact SET Date = @date, Info = @info WHERE ExternalId = @externalId", 
  new
  {
      Date = DateTime.UtcNow,      
      info = info.ToNVarChar(500),
      externalId = externalId.ToVarChar(100)
  });

DapperArgumentExtensions.cs

using Dapper;

/// <summary>
/// Extension methods for Dapper arguments
/// </summary>
/// <remarks>
/// The methods below are used to indicate the argument data type to Dapper and avoid the NVARCHAR(4000) arguments on SQL.
/// http://diegogiacomelli.com.br/dapper-and-the-nvarchar-4000-arguments
/// </remarks>
public static class DapperArgumentExtensions
{
    /// <summary>
    /// Builds a DbString argument as a VARCHAR.
    /// </summary>
    /// <param name="value">The argument value.</param>
    /// <param name="length">The argument length.</param>
    /// <returns>The configured DbString.</returns>
    public static DbString ToVarChar(this string value, int length)
    {
        return new DbString
        {
            Value = value,
            Length = length,
            IsAnsi = true,
            IsFixedLength = false
        };
    }

    /// <summary>
    /// Builds a DbString argument as a NVARCHAR.
    /// </summary>
    /// <param name="value">The argument value.</param>
    /// <param name="length">The argument length.</param>
    /// <returns>The configured DbString.</returns>
    public static DbString ToNVarChar(this string value, int length)
    {
        return new DbString
        {
            Value = value,
            Length = length,
            IsAnsi = false,
            IsFixedLength = false
        };
    }
}