Dapper/Npgsql stored procedure with refcursor parameter query

Question

I am using Dapper ( and I couldn't be happier), I know how to access normal stored procedures as mentioned here , however, how do I pass on the the Npgsql refcursor name to the proc (using C#)? For example:

I have a proc that looks like:

FUNCTION xx.getData(
    v_ref refcursor,
    v_id integer)
  RETURNS refcursor AS
...

How would I specify the parameters for xx.getData ?

For example, if getData accepted just one parameter of type int, then I could call it like so:

var data = cnn.Query<myType>("xx.getData", new {Id = 1}, 
        commandType: CommandType.StoredProcedure);

OR

var p = new DynamicParameters();
p.Add("@id", 11);
cnn.Execute("xx.getData", p, commandType: CommandType.StoredProcedure); 

I can't find the correct type in System.DbType to pass on in the query.

Answer 1

Note that a refcursor corresponds to an active cursor that has already been opened in a previous call. In other words, it does not correspond to a stored procedure, but rather to a resultset (possibly but not necessarily returned from a stored procedure).

Just in case you really do need to send a refcursor, what you're looking for is NpgsqlDbType.Refcursor .

Answer 2

Bellow custom dynamic parameter compatible for Npgsql data types. It will work for with output refcursor parameters.

/// <summary>
/// Npgsql Dynamic Param for Dapper
/// </summary>
public class PgParam : SqlMapper.IDynamicParameters
{
    private static readonly Dictionary<SqlMapper.Identity, Action<IDbCommand, object>> paramReaderCache = new Dictionary<SqlMapper.Identity, Action<IDbCommand, object>>();
    private readonly Dictionary<string, ParamInfo> _parameters = new Dictionary<string, ParamInfo>();
    private List<object> templates;

    /// <summary>
    ///     construct a dynamic parameter bag
    /// </summary>
    public PgParam()
    {
    }

    /// <summary>
    ///     construct a dynamic parameter bag
    /// </summary>
    /// <param name="template">can be an anonymous type or a DynamicParameters bag</param>
    public PgParam(object template)
    {
        AddDynamicParams(template);
    }

    /// <summary>
    ///     All the names of the param in the bag, use Get to yank them out
    /// </summary>
    public IEnumerable<string> ParameterNames
    {
        get { return _parameters.Select(p => p.Key); }
    }

    void SqlMapper.IDynamicParameters.AddParameters(IDbCommand command, SqlMapper.Identity identity)
    {
        AddParameters(command, identity);
    }

    /// <summary>
    ///     Append a whole object full of params to the dynamic
    ///     EG: AddDynamicParams(new {A = 1, B = 2}) // will add property A and B to the dynamic
    /// </summary>
    /// <param name="param"></param>
    public void AddDynamicParams(

        dynamic param
    )
    {
        if (param is object obj)
        {
            if (!(obj is PgParam subDynamic))
            {
                if (!(obj is IEnumerable<KeyValuePair<string, object>> dictionary))
                {
                    templates = templates ?? new List<object>();
                    templates.Add(obj);
                }
                else
                {
                    foreach (var kvp in dictionary)
                    {
                        Add(kvp.Key, kvp.Value);

                    }
                }
            }
            else
            {
                if (subDynamic._parameters != null)
                    foreach (var kvp in subDynamic._parameters)
                        _parameters.Add(kvp.Key, kvp.Value);

                if (subDynamic.templates != null)
                {
                    templates = templates ?? new List<object>();
                    foreach (var t in subDynamic.templates) templates.Add(t);
                }
            }
        }
    }

    /// <summary>
    ///     Add a parameter to this dynamic parameter list
    /// </summary>
    /// <param name="name"></param>
    /// <param name="value"></param>
    /// <param name="dbType"></param>
    /// <param name="direction"></param>
    /// <param name="size"></param>
    public void Add(string name, object value = null, NpgsqlDbType? dbType = null, ParameterDirection? direction = null,int? size = null)
    {
        _parameters[name] = new ParamInfo
        {
            Name = name, Value = value, ParameterDirection = direction ?? ParameterDirection.Input, DbType = dbType,
            Size = size
        };
    }


    /// <summary>
    ///     Add all the parameters needed to the command just before it executes
    /// </summary>
    /// <param name="command">The raw command prior to execution</param>
    /// <param name="identity">Information about the query</param>
    protected void AddParameters(IDbCommand command, SqlMapper.Identity identity)
    {
        if (templates != null)
            foreach (var template in templates)
            {
                var newIdent = identity.ForDynamicParameters(template.GetType());
                Action<IDbCommand, object> appender;

                lock (paramReaderCache)
                {
                    if (!paramReaderCache.TryGetValue(newIdent, out appender))
                    {
                        appender = SqlMapper.CreateParamInfoGenerator(newIdent, false, true);
                        paramReaderCache[newIdent] = appender;
                    }
                }

                appender(command, template);
            }

        foreach (var param in _parameters.Values)
        {

            var add = !((NpgsqlCommand) command).Parameters.Contains(param.Name);
            NpgsqlParameter p;
            if (add)
            {
                p = ((NpgsqlCommand) command).CreateParameter();
                p.ParameterName = param.Name;
            }
            else
            {
                p = ((NpgsqlCommand) command).Parameters[param.Name];
            }

            var val = param.Value;
            p.Value = val ?? DBNull.Value;
            p.Direction = param.ParameterDirection;
            if (param.Size != null) p.Size = param.Size.Value;
            if (param.DbType != null) p.NpgsqlDbType = param.DbType.Value;
            if (add) command.Parameters.Add(p);
            param.AttachedParam = p;
        }
    }

    /// <summary>
    ///     Get the value of a parameter
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="name"></param>
    /// <returns>The value, note DBNull.Value is not returned, instead the value is returned as null</returns>
    public T Get<T>(string name)
    {
        var val = _parameters[name].AttachedParam.Value;
        if (val == DBNull.Value)
        {
            if (default(T) != null)
                throw new ApplicationException("Attempting to cast a DBNull to a non nullable type!");
            return default(T);
        }

        return (T) val;
    }

    private class ParamInfo
    {
        public string Name { get; set; }

        public object Value { get; set; }

        public ParameterDirection ParameterDirection { get; set; }

        public NpgsqlDbType? DbType { get; set; }

        public int? Size { get; set; }

        public IDbDataParameter AttachedParam { get; set; }
    }
}