Massive.PostgreSQL.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Configuration;
using System.Data;
using System.Data.Common;
using System.Dynamic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.Text.RegularExpressions;

namespace Massive.PostgreSQL
{
    public static class ObjectExtensions
    {
        /// <summary>
        /// Extension method for adding in a bunch of parameters
        /// </summary>
        public static void AddParams(this DbCommand cmd, params object[] args)
        {
            foreach (var item in args)
            {
                AddParam(cmd, item);
            }
        }
        /// <summary>
        /// Extension for adding single parameter
        /// </summary>
        public static void AddParam(this DbCommand cmd, object item)
        {
            var p = cmd.CreateParameter();
            p.ParameterName = string.Format("@{0}", cmd.Parameters.Count);
            if (item == null)
            {
                p.Value = DBNull.Value;
            }
            else
            {
                if (item.GetType() == typeof(Guid))
                {
                    p.Value = item.ToString();
                    p.DbType = DbType.String;
                    p.Size = 4000;
                }
                else if (item.GetType() == typeof(ExpandoObject))
                {
                    var d = (IDictionary<string, object>)item;
                    p.Value = d.Values.FirstOrDefault();
                }
                else
                {
                    p.Value = item;
                }
                if (item.GetType() == typeof(string))
                    p.Size = ((string)item).Length > 4000 ? -1 : 4000;
            }
            cmd.Parameters.Add(p);
        }
        /// <summary>
        /// Turns an IDataReader to a Dynamic list of things
        /// </summary>
        public static List<dynamic> ToExpandoList(this IDataReader rdr)
        {
            var result = new List<dynamic>();
            while (rdr.Read())
            {
                result.Add(rdr.RecordToExpando());
            }
            return result;
        }
        public static dynamic RecordToExpando(this IDataReader rdr)
        {
            dynamic e = new ExpandoObject();
            var d = e as IDictionary<string, object>;
            for (int i = 0; i < rdr.FieldCount; i++)
                d.Add(rdr.GetName(i), DBNull.Value.Equals(rdr[i]) ? null : rdr[i]);
            return e;
        }
        /// <summary>
        /// Turns the object into an ExpandoObject
        /// </summary>
        public static dynamic ToExpando(this object o)
        {
            var result = new ExpandoObject();
            var d = result as IDictionary<string, object>; //work with the Expando as a Dictionary
            if (o.GetType() == typeof(ExpandoObject)) return o; //shouldn't have to... but just in case
            if (o.GetType() == typeof(NameValueCollection) || o.GetType().IsSubclassOf(typeof(NameValueCollection)))
            {
                var nv = (NameValueCollection)o;
                nv.Cast<string>().Select(key => new KeyValuePair<string, object>(key, nv[key])).ToList().ForEach(i => d.Add(i));
            }
            else
            {
                var props = o.GetType().GetProperties();
                foreach (var item in props)
                {
                    d.Add(item.Name, item.GetValue(o, null));
                }
            }
            return result;
        }

        /// <summary>
        /// Turns the object into a Dictionary
        /// </summary>
        public static IDictionary<string, object> ToDictionary(this object thingy)
        {
            return (IDictionary<string, object>)thingy.ToExpando();
        }
    }

    /// <summary>
    /// Convenience class for opening/executing data
    /// </summary>
    public static class DB
    {
        public static DynamicModel Current
        {
            get
            {
                if (ConfigurationManager.ConnectionStrings.Count > 1)
                {
                    return new DynamicModel(ConfigurationManager.ConnectionStrings[1].Name);
                }
                throw new InvalidOperationException("Need a connection string name - can't determine what it is");
            }
        }
    }

    /// <summary>
    /// A class that wraps your database table in Dynamic Funtime
    /// </summary>
    public class DynamicModel : DynamicObject
    {
        DbProviderFactory _factory;
        string ConnectionString;
        public static DynamicModel Open(string connectionStringName)
        {
            dynamic dm = new DynamicModel(connectionStringName);
            return dm;
        }
        public DynamicModel(string connectionStringName, string tableName = "",
            string primaryKeyField = "", string descriptorField = "")
        {
            TableName = tableName == "" ? this.GetType().Name : tableName;
            PrimaryKeyField = string.IsNullOrEmpty(primaryKeyField) ? "ID" : primaryKeyField;
            DescriptorField = descriptorField;
            var _providerName = "Npgsql";
            _factory = DbProviderFactories.GetFactory(_providerName);
            ConnectionString = ConfigurationManager.ConnectionStrings[connectionStringName].ConnectionString;
        }

        /// <summary>
        /// Creates a new Expando from a Form POST - white listed against the columns in the DB
        /// </summary>
        public dynamic CreateFrom(NameValueCollection coll)
        {
            dynamic result = new ExpandoObject();
            var dc = (IDictionary<string, object>)result;
            var schema = Schema;
            //loop the collection, setting only what's in the Schema
            foreach (var item in coll.Keys)
            {
                var exists = schema.Any(x => x.COLUMN_NAME.ToLower() == item.ToString().ToLower());
                if (exists)
                {
                    var key = item.ToString();
                    var val = coll[key];
                    dc.Add(key, val);
                }
            }
            return result;
        }
        /// <summary>
        /// Gets a default value for the column
        /// </summary>
        public dynamic DefaultValue(dynamic column)
        {
            dynamic result = null;
            string def = column.COLUMN_DEFAULT;
            if (String.IsNullOrEmpty(def))
            {
                result = null;
            }
            else if (def == "getdate()" || def == "(getdate())")
            {
                result = DateTime.Now.ToShortDateString();
            }
            else if (def == "newid()")
            {
                result = Guid.NewGuid().ToString();
            }
            else
            {
                result = def.Replace("(", "").Replace(")", "");
            }
            return result;
        }
        /// <summary>
        /// Creates an empty Expando set with defaults from the DB
        /// </summary>
        public dynamic Prototype
        {
            get
            {
                dynamic result = new ExpandoObject();
                var schema = Schema;
                foreach (dynamic column in schema)
                {
                    var dc = (IDictionary<string, object>)result;
                    dc.Add(column.COLUMN_NAME, DefaultValue(column));
                }
                result._Table = this;
                return result;
            }
        }
        public string DescriptorField { get; protected set; }
        /// <summary>
        /// List out all the schema bits for use with ... whatever
        /// </summary>
        IEnumerable<dynamic> _schema;
        public IEnumerable<dynamic> Schema
        {
            get
            {
                if (_schema == null)
                    _schema = Query("SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = @0", TableName);
                return _schema;
            }
        }

        /// <summary>
        /// Enumerates the reader yielding the result - thanks to Jeroen Haegebaert
        /// </summary>
        public virtual IEnumerable<dynamic> Query(string sql, params object[] args)
        {
            using (var conn = OpenConnection())
            {
                var rdr = CreateCommand(sql, conn, args).ExecuteReader();
                while (rdr.Read())
                {
                    yield return rdr.RecordToExpando(); ;
                }
            }
        }
        public virtual IEnumerable<dynamic> Query(string sql, DbConnection connection, params object[] args)
        {
            using (var rdr = CreateCommand(sql, connection, args).ExecuteReader())
            {
                while (rdr.Read())
                {
                    yield return rdr.RecordToExpando(); ;
                }
            }
        }
        /// <summary>
        /// Returns a single result
        /// </summary>
        public virtual object Scalar(string sql, params object[] args)
        {
            object result = null;
            using (var conn = OpenConnection())
            {
                result = CreateCommand(sql, conn, args).ExecuteScalar();
            }
            return result;
        }
        /// <summary>
        /// Creates a DBCommand that you can use for loving your database.
        /// </summary>
        DbCommand CreateCommand(string sql, DbConnection conn, params object[] args)
        {
            var result = _factory.CreateCommand();
            result.Connection = conn;
            result.CommandText = sql;
            if (args.Length > 0)
                result.AddParams(args);
            return result;
        }
        /// <summary>
        /// Returns and OpenConnection
        /// </summary>
        public virtual DbConnection OpenConnection()
        {
            var result = _factory.CreateConnection();
            result.ConnectionString = ConnectionString;
            result.Open();
            return result;
        }
        /// <summary>
        /// Builds a set of Insert and Update commands based on the passed-on objects.
        /// These objects can be POCOs, Anonymous, NameValueCollections, or Expandos. Objects
        /// With a PK property (whatever PrimaryKeyField is set to) will be created at UPDATEs
        /// </summary>
        public virtual List<DbCommand> BuildCommands(params object[] things)
        {
            var commands = new List<DbCommand>();
            foreach (var item in things)
            {
                if (HasPrimaryKey(item))
                {
                    commands.Add(CreateUpdateCommand(item, GetPrimaryKey(item)));
                }
                else
                {
                    commands.Add(CreateInsertCommand(item));
                }
            }
            return commands;
        }


        public virtual int Execute(DbCommand command)
        {
            return Execute(new DbCommand[] { command });
        }

        public virtual int Execute(string sql, params object[] args)
        {
            return Execute(CreateCommand(sql, null, args));
        }
        /// <summary>
        /// Executes a series of DBCommands in a transaction
        /// </summary>
        public virtual int Execute(IEnumerable<DbCommand> commands)
        {
            var result = 0;
            using (var conn = OpenConnection())
            {
                using (var tx = conn.BeginTransaction())
                {
                    foreach (var cmd in commands)
                    {
                        cmd.Connection = conn;
                        cmd.Transaction = tx;
                        result += cmd.ExecuteNonQuery();
                    }
                    tx.Commit();
                }
            }
            return result;
        }
        public virtual string PrimaryKeyField { get; set; }
        /// <summary>
        /// Conventionally introspects the object passed in for a field that 
        /// looks like a PK. If you've named your PrimaryKeyField, this becomes easy
        /// </summary>
        public virtual bool HasPrimaryKey(object o)
        {
            return o.ToDictionary().ContainsKey(PrimaryKeyField);
        }
        /// <summary>
        /// If the object passed in has a property with the same name as your PrimaryKeyField
        /// it is returned here.
        /// </summary>
        public virtual object GetPrimaryKey(object o)
        {
            object result = null;
            o.ToDictionary().TryGetValue(PrimaryKeyField, out result);
            return result;
        }
        public virtual string TableName { get; set; }
        /// <summary>
        /// Returns all records complying with the passed-in WHERE clause and arguments, 
        /// ordered as specified, limited (TOP) by limit.
        /// </summary>
        public virtual IEnumerable<dynamic> All(string where = "", string orderBy = "", int limit = 0, string columns = "*", params object[] args)
        {
            string sql = BuildSelect(where, orderBy, limit);
            return Query(string.Format(sql, columns, TableName), args);
        }
        private static string BuildSelect(string where, string orderBy, int limit)
        {
            string sql = "SELECT {0} FROM {1} ";
            if (!string.IsNullOrEmpty(where))
                sql += where.Trim().StartsWith("where", StringComparison.OrdinalIgnoreCase) ? where : " WHERE " + where;
            if (!String.IsNullOrEmpty(orderBy))
                sql += orderBy.Trim().StartsWith("order by", StringComparison.OrdinalIgnoreCase) ? orderBy : " ORDER BY " + orderBy;
            if (limit > 0)
                sql += " LIMIT " + limit;
            return sql;
        }

        /// <summary>
        /// Returns a dynamic PagedResult. Result properties are Items, TotalPages, and TotalRecords.
        /// </summary>
        public virtual dynamic Paged(string where = "", string orderBy = "", string columns = "*", int pageSize = 20, int currentPage = 1, params object[] args)
        {
            return BuildPagedResult(where: where, orderBy: orderBy, columns: columns, pageSize: pageSize, currentPage: currentPage, args: args);
        }

        public virtual dynamic Paged(string sql, string primaryKey, string where = "", string orderBy = "", string columns = "*", int pageSize = 20, int currentPage = 1, params object[] args)
        {
            return BuildPagedResult(sql, primaryKey, where, orderBy, columns, pageSize, currentPage, args);
        }

        private dynamic BuildPagedResult(string sql = "", string primaryKeyField = "", string where = "", string orderBy = "", string columns = "*", int pageSize = 20, int currentPage = 1, params object[] args)
        {
            dynamic result = new ExpandoObject();
            var countSQL = "";
            if (!string.IsNullOrEmpty(sql))
                countSQL = string.Format("SELECT COUNT({0}) FROM ({1}) AS PagedTable", primaryKeyField, sql);
            else
                countSQL = string.Format("SELECT COUNT({0}) FROM {1}", PrimaryKeyField, TableName);

            if (String.IsNullOrEmpty(orderBy))
            {
                orderBy = string.IsNullOrEmpty(primaryKeyField) ? " ORDER BY " + PrimaryKeyField : " ORDER BY " + primaryKeyField;
            }

            if (!string.IsNullOrEmpty(where))
            {
                if (!where.Trim().StartsWith("where", StringComparison.CurrentCultureIgnoreCase))
                {
                    where = " WHERE " + where;
                }
            }

            var query = "";
            if (!string.IsNullOrEmpty(sql))
                query = string.Format("{0} {1} {2} ", sql, where, orderBy);
            else
                query = string.Format("SELECT {0} FROM {1} {2} {3} ", columns, TableName, where, orderBy);

            var pageStart = (currentPage - 1) * pageSize;
            query += string.Format(" limit {0} offset {1}", pageSize, pageStart);
            countSQL += where;
            result.TotalRecords = Scalar(countSQL, args);
            result.TotalPages = result.TotalRecords / pageSize;
            if (result.TotalRecords % pageSize > 0)
                result.TotalPages += 1;
            result.Items = Query(string.Format(query, columns, TableName), args);
            return result;
        }
        /// <summary>
        /// Returns a single row from the database
        /// </summary>
        public virtual dynamic Single(string where, params object[] args)
        {
            var sql = string.Format("SELECT * FROM {0} WHERE {1}", TableName, where);
            return Query(sql, args).FirstOrDefault();
        }
        /// <summary>
        /// Returns a single row from the database
        /// </summary>
        public virtual dynamic Single(object key, string columns = "*")
        {
            var sql = string.Format("SELECT {0} FROM {1} WHERE {2} = @0", columns, TableName, PrimaryKeyField);
            return Query(sql, key).FirstOrDefault();
        }
        /// <summary>
        /// This will return a string/object dictionary for dropdowns etc
        /// </summary>
        public virtual IDictionary<string, object> KeyValues(string orderBy = "")
        {
            if (String.IsNullOrEmpty(DescriptorField))
                throw new InvalidOperationException("There's no DescriptorField set - do this in your constructor to describe the text value you want to see");
            var sql = string.Format("SELECT {0},{1} FROM {2} ", PrimaryKeyField, DescriptorField, TableName);
            if (!String.IsNullOrEmpty(orderBy))
                sql += "ORDER BY " + orderBy;

            var results = Query(sql).ToList().Cast<IDictionary<string, object>>();
            return results.ToDictionary(key => key[PrimaryKeyField].ToString(), value => value[DescriptorField]);
        }

        /// <summary>
        /// This will return an Expando as a Dictionary
        /// </summary>
        public virtual IDictionary<string, object> ItemAsDictionary(ExpandoObject item)
        {
            return (IDictionary<string, object>)item;
        }
        //Checks to see if a key is present based on the passed-in value
        public virtual bool ItemContainsKey(string key, ExpandoObject item)
        {
            var dc = ItemAsDictionary(item);
            return dc.ContainsKey(key);
        }
        /// <summary>
        /// Executes a set of objects as Insert or Update commands based on their property settings, within a transaction.
        /// These objects can be POCOs, Anonymous, NameValueCollections, or Expandos. Objects
        /// With a PK property (whatever PrimaryKeyField is set to) will be created at UPDATEs
        /// </summary>
        public virtual int Save(params object[] things)
        {
            foreach (var item in things)
            {
                if (!IsValid(item))
                {
                    throw new InvalidOperationException("Can't save this item: " + String.Join("; ", Errors.ToArray()));
                }
            }
            var commands = BuildCommands(things);
            return Execute(commands);
        }
        public virtual DbCommand CreateInsertCommand(dynamic expando)
        {
            DbCommand result = null;
            var settings = (IDictionary<string, object>)expando;
            var sbKeys = new StringBuilder();
            var sbVals = new StringBuilder();
            var stub = "INSERT INTO {0} ({1}) \r\n VALUES ({2})";
            result = CreateCommand(stub, null);
            int counter = 0;
            foreach (var item in settings)
            {
                sbKeys.AppendFormat("{0},", item.Key);
                sbVals.AppendFormat("@{0},", counter.ToString());
                result.AddParam(item.Value);
                counter++;
            }
            if (counter > 0)
            {
                var keys = sbKeys.ToString().Substring(0, sbKeys.Length - 1);
                var vals = sbVals.ToString().Substring(0, sbVals.Length - 1);
                var sql = string.Format(stub, TableName, keys, vals);
                result.CommandText = sql;
            }
            else throw new InvalidOperationException("Can't parse this object to the database - there are no properties set");
            return result;
        }
        /// <summary>
        /// Creates a command for use with transactions - internal stuff mostly, but here for you to play with
        /// </summary>
        public virtual DbCommand CreateUpdateCommand(dynamic expando, object key)
        {
            var settings = (IDictionary<string, object>)expando;
            var sbKeys = new StringBuilder();
            var stub = "UPDATE {0} SET {1} WHERE {2} = @{3}";
            var args = new List<object>();
            var result = CreateCommand(stub, null);
            int counter = 0;
            foreach (var item in settings)
            {
                var val = item.Value;
                if (!item.Key.Equals(PrimaryKeyField, StringComparison.OrdinalIgnoreCase) && item.Value != null)
                {
                    result.AddParam(val);
                    sbKeys.AppendFormat("{0} = @{1}, \r\n", item.Key, counter.ToString());
                    counter++;
                }
            }
            if (counter > 0)
            {
                //add the key
                result.AddParam(key);
                //strip the last commas
                var keys = sbKeys.ToString().Substring(0, sbKeys.Length - 4);
                result.CommandText = string.Format(stub, TableName, keys, PrimaryKeyField, counter);
            }
            else throw new InvalidOperationException("No parsable object was sent in - could not divine any name/value pairs");
            return result;
        }
        /// <summary>
        /// Removes one or more records from the DB according to the passed-in WHERE
        /// </summary>
        public virtual DbCommand CreateDeleteCommand(string where = "", object key = null, params object[] args)
        {
            var sql = string.Format("DELETE FROM {0} ", TableName);
            if (key != null)
            {
                sql += string.Format("WHERE {0}=@0", PrimaryKeyField);
                args = new object[] { key };
            }
            else if (!string.IsNullOrEmpty(where))
            {
                sql += where.Trim().StartsWith("where", StringComparison.OrdinalIgnoreCase) ? where : "WHERE " + where;
            }
            return CreateCommand(sql, null, args);
        }

        public bool IsValid(dynamic item)
        {
            Errors.Clear();
            Validate(item);
            return Errors.Count == 0;
        }

        //Temporary holder for error messages
        public IList<string> Errors = new List<string>();
        /// <summary>
        /// Adds a record to the database. You can pass in an Anonymous object, an ExpandoObject,
        /// A regular old POCO, or a NameValueColletion from a Request.Form or Request.QueryString
        /// </summary>
        public virtual dynamic Insert(object o)
        {
            var ex = o.ToExpando();
            if (!IsValid(ex))
            {
                throw new InvalidOperationException("Can't insert: " + String.Join("; ", Errors.ToArray()));
            }
            if (BeforeSave(ex))
            {
                using (dynamic conn = OpenConnection())
                {
                    var cmd = CreateInsertCommand(ex);
                    cmd.Connection = conn;
                    cmd.CommandText += String.Format(" returning {0} as newid ", PrimaryKeyField);
                    ex.ID = cmd.ExecuteScalar();
                    Inserted(ex);
                }
                return ex;
            }
            else
            {
                return null;
            }
        }
        /// <summary>
        /// Updates a record in the database. You can pass in an Anonymous object, an ExpandoObject,
        /// A regular old POCO, or a NameValueCollection from a Request.Form or Request.QueryString
        /// </summary>
        public virtual int Update(object o, object key)
        {
            var ex = o.ToExpando();
            if (!IsValid(ex))
            {
                throw new InvalidOperationException("Can't Update: " + String.Join("; ", Errors.ToArray()));
            }
            var result = 0;
            if (BeforeSave(ex))
            {
                result = Execute(CreateUpdateCommand(ex, key));
                Updated(ex);
            }
            return result;
        }
        /// <summary>
        /// Removes one or more records from the DB according to the passed-in WHERE
        /// </summary>
        public int Delete(object key = null, string where = "", params object[] args)
        {
            var deleted = this.Single(key);
            var result = 0;
            if (BeforeDelete(deleted))
            {
                result = Execute(CreateDeleteCommand(where: where, key: key, args: args));
                Deleted(deleted);
            }
            return result;
        }

        public void DefaultTo(string key, object value, dynamic item)
        {
            if (!ItemContainsKey(key, item))
            {
                var dc = (IDictionary<string, object>)item;
                dc[key] = value;
            }
        }

        //Hooks
        public virtual void Validate(dynamic item) { }
        public virtual void Inserted(dynamic item) { }
        public virtual void Updated(dynamic item) { }
        public virtual void Deleted(dynamic item) { }
        public virtual bool BeforeDelete(dynamic item) { return true; }
        public virtual bool BeforeSave(dynamic item) { return true; }

        //validation methods
        public virtual void ValidatesPresenceOf(object value, string message = "Required")
        {
            if (value == null)
                Errors.Add(message);
            if (String.IsNullOrEmpty(value.ToString()))
                Errors.Add(message);
        }
        //fun methods
        public virtual void ValidatesNumericalityOf(object value, string message = "Should be a number")
        {
            var type = value.GetType().Name;
            var numerics = new string[] { "Int32", "Int16", "Int64", "Decimal", "Double", "Single", "Float" };
            if (!numerics.Contains(type))
            {
                Errors.Add(message);
            }
        }
        public virtual void ValidateIsCurrency(object value, string message = "Should be money")
        {
            if (value == null)
                Errors.Add(message);
            decimal val = decimal.MinValue;
            decimal.TryParse(value.ToString(), out val);
            if (val == decimal.MinValue)
                Errors.Add(message);


        }
        public int Count()
        {
            return Count(TableName);
        }
        public int Count(string tableName, string where = "")
        {
            // Scalar returns a long that has been casted to an object. Casting a boxed
            // long directly to int throws InvalidCastException. This will successfully
            // cast without changing the API.
            // HACK: Change API so count returns long
            return (int)(long)Scalar("SELECT COUNT(*) FROM " + tableName + " " + where);
        }

        /// <summary>
        /// A helpful query tool
        /// </summary>
        public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
        {
            //parse the method
            var constraints = new List<string>();
            var counter = 0;
            var info = binder.CallInfo;
            // accepting named args only... SKEET!
            if (info.ArgumentNames.Count != args.Length)
            {
                throw new InvalidOperationException("Please use named arguments for this type of query - the column name, orderby, columns, etc");
            }
            //first should be "FindBy, Last, Single, First"
            var op = binder.Name;
            var columns = " * ";
            string orderBy = string.Format(" ORDER BY {0}", PrimaryKeyField);
            string sql = "";
            string where = "";
            var whereArgs = new List<object>();

            //loop the named args - see if we have order, columns and constraints
            if (info.ArgumentNames.Count > 0)
            {

                for (int i = 0; i < args.Length; i++)
                {
                    var name = info.ArgumentNames[i].ToLower();
                    switch (name)
                    {
                        case "orderby":
                            orderBy = " ORDER BY " + args[i];
                            break;
                        case "columns":
                            columns = args[i].ToString();
                            break;
                        default:
                            constraints.Add(string.Format(" {0} = @{1}", name, counter));
                            whereArgs.Add(args[i]);
                            counter++;
                            break;
                    }
                }
            }

            //Build the WHERE bits
            if (constraints.Count > 0)
            {
                where = " WHERE " + string.Join(" AND ", constraints.ToArray());  //This doesn't work so hot. turns into Where =@0 instead of actual arg
            }
            //probably a bit much here but... yeah this whole thing needs to be refactored...
            if (op.ToLower() == "count")
            {
                result = Scalar("SELECT COUNT(*) FROM " + TableName + where, whereArgs.ToArray());
            }
            else if (op.ToLower() == "sum")
            {
                result = Scalar("SELECT SUM(" + columns + ") FROM " + TableName + where, whereArgs.ToArray());
            }
            else if (op.ToLower() == "max")
            {
                result = Scalar("SELECT MAX(" + columns + ") FROM " + TableName + where, whereArgs.ToArray());
            }
            else if (op.ToLower() == "min")
            {
                result = Scalar("SELECT MIN(" + columns + ") FROM " + TableName + where, whereArgs.ToArray());
            }
            else if (op.ToLower() == "avg")
            {
                result = Scalar("SELECT AVG(" + columns + ") FROM " + TableName + where, whereArgs.ToArray());
            }
            else
            {

                //build the SQL
                sql = "SELECT " + columns + " FROM " + TableName + where + " limit 1;";
                var justOne = op.StartsWith("First") || op.StartsWith("Last") || op.StartsWith("Get") || op.StartsWith("Single");

                //Be sure to sort by DESC on the PK (PK Sort is the default)
                if (op.StartsWith("Last"))
                {
                    orderBy = orderBy + " DESC ";
                }
                else
                {
                    //default to multiple
                    sql = "SELECT " + columns + " FROM " + TableName + where;
                }

                if (justOne)
                {
                    //return a single record
                    result = Query(sql + orderBy, whereArgs.ToArray()).FirstOrDefault();
                }
                else
                {
                    //return lots
                    result = Query(sql + orderBy, whereArgs.ToArray());
                }
            }
            return true;
        }
    }
}