Patterns: Fluent Interface - make your code easier to read

Sep 27, 2007 • Design Patterns

I never heard of the Fluent Interface pattern until I saw Randy Patterson’s blog post titled “How to design a Fluent Interface”. When I first saw the title of the post I thought he was talking about design a user interface, but upon further inspection I found out that using the Fluent Interface pattern in your code will make it easier to read.

Randy posts an example of how to use the Fluent Interface pattern, but I thought I would also write up a short example. My example below shows how to implement a small class to generate Sql scripts using the Fluent Interface pattern.

Example Usage:

SQLQuery sql = new SQLQuery();
sql.Select(”Id”).Select(”FirstName”).Select(”LastName”).From(”Person”).Where(”Id = 1”).Where(”FirstName = ‘Chris’”).OrderBy(”LastName”).OrderBy(”FirstName”);

/// Get the string representation of our Sql query
string strSqlString = sql.ToString();

Console.WriteLine(strSqlString);

Code for the SQLQuery class:

public class SQLQuery
{
private ArrayList _SelectItems = new ArrayList();
private ArrayList _WhereItems = new ArrayList();
private ArrayList _OrderByItems = new ArrayList();
private string _FromTable = null;

public SQLQuery Select(string select)
{
_SelectItems.Add(select);
return this;
}

public SQLQuery From(string from)
{
_FromTable = from;
return this;
}

public SQLQuery Where(string where)
{
_WhereItems.Add(where);
return this;
}

public SQLQuery OrderBy(string orderby)
{
_OrderByItems.Add(orderby);
return this;
}

public override string ToString()
{
StringBuilder sb = new StringBuilder();

sb.Append(”SELECT “);
for(int i = 0; i < _SelectItems.Count; i++)
sb.Append(_SelectItems[i] + ((i == _SelectItems.Count - 1) ? ” “ : ”, “));

sb.Append(”FROM “);
sb.Append(_FromTable);

sb.Append(” WHERE “);
for(int i = 0; i < _WhereItems.Count; i++)
sb.Append(_WhereItems[i] + ((i == _WhereItems.Count - 1) ? ” “ : ” AND “));

sb.Append(”ORDER BY “);
for(int i = 0; i < _OrderByItems.Count; i++)
sb.Append(_OrderByItems[i] + ((i == _OrderByItems.Count - 1) ? ” “ : ”, “));

return sb.ToString();
}
}