【2016-11-15】【坚持学习】【Day26】【通用的SQLHelper】

今天看DevDemo源码时候看到一个写得很好的SQLHelper

代码

  public class SqlHelper<T, Command>
        where T : DbConnection
        where Command : DbCommand, new() {
        public object ReadValue(T connection, string selectQuery, params DbParameter[] pars) {
            using(var sql = CreateCommand(selectQuery, connection)) {
                sql.CommandTimeout = ;
                if(pars != null)
                    sql.Parameters.AddRange(pars);
                try {
                    return CheckDbNull(sql.ExecuteScalar());
                }
                catch { return null; }
            }
        }
        object CheckDbNull(object value) {
            if(value == null) return null;
            if(Object.ReferenceEquals(value, DBNull.Value)) return null;
            return value;
        }
        static DbCommand CreateCommand(string selectQuery, T connection) {
            return new Command() { CommandText = selectQuery, Connection = connection };
        }
        public List<object[]> ReadValues(T connection, string selectQuery, params DbParameter[] pars) {
            List<object[]> res = new List<object[]>();
            try {
                using(var sql = CreateCommand(selectQuery, connection)) {
                    sql.CommandTimeout = ;
                    if(pars != null) sql.Parameters.AddRange(pars);
                    using(DbDataReader reader = sql.ExecuteReader()) {
                        if(!reader.HasRows) return res;
                        while(reader.Read()) {
                            object[] values = new object[reader.FieldCount];
                            reader.GetValues(values);
                            res.Add(values);
                        }
                    }
                }
            }
            catch { }
            return res;
        }
        public string GetString(object val) {
            if(val == DBNull.Value || val == null) return string.Empty;
            return val.ToString();
        }
        public DateTime GetDateInv(object val) {
            if(val == DBNull.Value || val == null) return DateTime.MinValue;
            return DateTime.ParseExact(val.ToString(), "d/M/yyyy", DateTimeFormatInfo.InvariantInfo);
        }
        public int GetInt(object val) {
            if(val == DBNull.Value || val == null) return ;
            return Convert.ToInt32(val);
        }
        public DateTime GetDate(object value) {
            if(value == null || value == DBNull.Value) return DateTime.MinValue;
            if(value is DateTime) return (DateTime)value;
            return GetDateInv(value);
        }
        public decimal GetDecimal(object value) {
            if(value == null || value == DBNull.Value) return ;
            return (decimal)Convert.ChangeType(value, typeof(decimal));
        }
        public Guid GetGuid(object value) {
            if(value == null || value == DBNull.Value) return Guid.Empty;
            return new Guid(value.ToString());
        }
        public bool GetBool(object value) {
            if(value == null || value == DBNull.Value) return false;
            if(value is bool) return (bool)value;
            if(value is int) return (int)value == ;
            return false;
        }
    }

   using (var connection = new OleDbConnection(connectionString))
            {
                connection.Open();
                //new OleDbCommand("delete * from sales", connection).ExecuteNonQuery(); //FOR TEST PURPOSES
                var helper = new SqlHelper<OleDbConnection, OleDbCommand>();
                DateTime minDate = helper.GetDate(helper.ReadValue(connection, "select min(sale_date) from sales"));
                DateTime maxDate = helper.GetDate(helper.ReadValue(connection, "select max(sale_date) from sales"));
                this.maxId = helper.GetInt(helper.ReadValue(connection, "select max(id) from sales"));
                DateTime startDate = minRequiredDate;
                if (minDate > startDate && maxDate != DateTime.MinValue)
                {
                    startDate = maxDate.AddDays();
                }
                if (startDate > DateTime.Today.AddDays())
                    return true;
                double daysCount = currentDate.Subtract(startDate).TotalDays;
                RaiseStart();
                try { Generate(connection, startDate, (int)daysCount); }
                finally { RaiseComplete(); }
                connection.Close();
            }