浅析如何优雅封装.NET数据库访问层

// A类
var sql = "SELECT * FROM A WHERE id=@id";

// B类
var sql = "SELECT * FROM A WHERE id=" + id;

cmd.Parameters.AddWithValue("@id", id);

Execute(sql, new { id = 1, name = "张三" });

public static int Execute(string sql, object param = null)
{
    using (var conn = new SqlConnection(connStr))
    {
        using (var cmd = new SqlCommand(sql, conn))
        {
            if (param != null)
            {
                AddParameters(cmd, param);
            }

            conn.Open();
            return cmd.ExecuteNonQuery();
        }
    }
}

public static T QueryFirst<T>(string sql, object param = null) where T : new()
{
    using (var conn = new SqlConnection(connStr))
    using (var cmd = new SqlCommand(sql, conn))
    {
        if (param != null)
        {
            AddParameters(cmd, param);
        }

        conn.Open();
        using (var reader = cmd.ExecuteReader())
        {
            if (!reader.Read()) return default;

            var obj = new T();
            foreach (var prop in typeof(T).GetProperties())
            {
                if (!reader.HasColumn(prop.Name)) continue;

                var val = reader[prop.Name];
                if (val != DBNull.Value)
                    prop.SetValue(obj, val);
            }

            return obj;
        }
    }
}

private static void AddParameters(SqlCommand cmd, object param)
{
    foreach (var prop in param.GetType().GetProperties())
    {
        var value = prop.GetValue(param) ?? DBNull.Value;
        cmd.Parameters.AddWithValue("@" + prop.Name, value);
    }
}

var sql = $"SELECT * FROM User WHERE Name='{name}'";

var sql = "SELECT * FROM User WHERE Name=@Name";
var user = QueryFirst<User>(sql, new { Name = name });

Stopwatch sw = Stopwatch.StartNew();

var result = cmd.ExecuteNonQuery();

sw.Stop();
Console.WriteLine($"SQL执行耗时：{sw.ElapsedMilliseconds}ms");
Console.WriteLine(sql);

int retry = 3;
while (retry-- > 0)
{
    try
    {
        return cmd.ExecuteNonQuery();
    }
    catch
    {
        if (retry == 0) throw;
        Thread.Sleep(200);
    }
}

public static void ExecuteInTransaction(Action<SqlConnection, SqlTransaction> action)
{
    using var conn = new SqlConnection(connStr);
    conn.Open();

    using var tran = conn.BeginTransaction();

    try
    {
        action(conn, tran);
        tran.Commit();
    }
    catch
    {
        tran.Rollback();
        throw;
    }
}

ExecuteInTransaction((conn, tran) =>
{
    Execute("INSERT ...", param1, conn, tran);
    Execute("UPDATE ...", param2, conn, tran);
});

var allowedColumns = new[] { "Name", "Age" };

if (!allowedColumns.Contains(column))
{
    throw new Exception("非法字段");
}