"SqlParameterCollection only accepts non-null SqlParameter type objects, not String objects"

I tried all the above-mentioned steps but nothing helps.

Finally found and fixed it by changing the namespace

using System.Data.SqlClient to using Microsoft.Data.SqlClient

Arshad

I had been getting the same error and had to use AddWithValue like this...

cmd.Parameters.AddWithValue(@columnToUpdate, newValue);
cmd.Parameters.AddWithValue(@conditionalColumn, conditionalValue);

I replaced my reference to System.Data.SqlClient with Microsoft.Data.SqlClient corrected the using statements and my problems went away

In my .csproj I now have

  <ItemGroup>
    <PackageReference Include="Microsoft.Data.SqlClient" Version="1.1.2" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.1.3" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.3" />
  </ItemGroup>

But I also found I had use of the following scenario where I created a System.Data.SqlClient.SqlParameter

    public static List<T> RunQuery<T>(ApiDbContext context, string query, Func<DbDataReader, T> map, params SqlParameter[] parameters)
    {
        var cn = context.Database.GetDbConnection();
        var oldState = cn.State;
        if (cn.State.Equals(ConnectionState.Closed)) { cn.Open(); }

        using (var command = cn.CreateCommand())
        {
            command.CommandText = query;
            command.CommandType = CommandType.Text;
            foreach (var param in parameters)
            {
                var p = new System.Data.SqlClient.SqlParameter
                {
                    ParameterName = param.ParameterName, Value = param.Value, SqlDbType = param.SqlDbType
                };
                command.Parameters.Add(p);
            }
            if (cn.State.Equals(ConnectionState.Closed)) { cn.Open(); }
            var entities = new List<T>();
            using (var result = command.ExecuteReader())
            {
                while (result.Read())
                {
                    entities.Add(map(result));
                }
            }

            if (oldState.Equals(ConnectionState.Closed) && cn.State == ConnectionState.Open) { cn.Close(); }
            return entities;
        }
    }