LINQ query result with string manipulation and regex

Question

Context

I retrieve a list of sites from a database like this:

DashboardEntities dashboardDB = new DashboardEntities();

var sites = dashboardDB.Instances
    .Select(attr => new SiteModel
        {
            server = attr.server,
            pool = attr.pool,
            url = attr.url,
            version = attr.version,
            client = ???
        })
    .ToList();

return sites;

For client , I need to get a substring from the url like this:

String client = "";

Regex rgx = new Regex(@"\.[a-z-./]+");
client = rgx.Replace(attr.url, "");

rgx = new Regex("formation-");
client = rgx.Replace(client, "");

Question

How do this string manipulation with regex into my LINQ query?

Answer 1

According to Guffa and RePierre:

DashboardEntities dashboardDB = new DashboardEntities();

var sites = dashboardDB.Instances
    .Select(attr => new SiteModel
        {
            url = attr.url,
            server = attr.server,
            pool = attr.pool,
            version = attr.version,
            client = attr.url
        })
    .ToList();

sites.ForEach(attr => attr.client = Regex.Replace(attr.client, @"\.[a-z-./]+", "").Replace("formation-", ""));

Answer 2

You can't in the current form you have it. There will be no known translation to SQL for the regex portion. However, you could add it on as a subsequent select once the .ToList() is called.

...   .ToList()
      .Select(
          z => z.client = new Regex(@"\.[a-z-./]+")
               .Replace(z.attr.url, "").Replace("formation-", "")
      )

Treat that as pseudo code, but that general approach should be able to get it done. Then you'd just need to set client = "" in the initial select.

Edit: As a side note, the "formation-" piece really doesn't need to be a Regex. A simple string replace should suffice there and would be faster.

Answer 3

Unfortunatelly, you won't be able to send the regex processing logic directly to the database; you'll need to get the url from the database and then iterate over the list to get client data from the url.

DashboardEntities dashboardDB = new DashboardEntities();  
var sites = dashboardDB.Instances 
    .Select(attr => new SiteModel 
    { 
        server = attr.server, 
        pool = attr.pool, 
        url = attr.url, 
        version = attr.version, 
        client = attr.url    // load the url for further processing
    }) 
    .ToList();
// iterate over the list and get client data from the url
sites.ForEach(ite => item.client = GetSubstring(item.client)); 
return sites; 

Where the method GetSubstring encapsulates the regex processing logic.

private string GetSubstring(string url)
{
    String client = "";        
    Regex rgx = new Regex(@"\.[a-z-./]+");        
    client = rgx.Replace(attr.url, "");        
    rgx = new Regex("formation-");        
    client = rgx.Replace(client, ""); 
    return client;
}

Answer 4

There might be better ways, but what about:

Regex rgx1 = new Regex(@"\.[a-z-./]+");
Regex rgx2 = new Regex("formation-");

DashboardEntities dashboardDB = new DashboardEntities();

var sites = dashboardDB.Instances
    .Select(attr => new SiteModel
        {
            server = attr.server,
            pool = attr.pool,
            url = attr.url,
            version = attr.version,
            client = rgx2.Replace(rgx1.Replace(attr.url,""),"")
        })
    .ToList();

return sites;

Answer 5

You don't even need a regular expression for the second replace. You can do it as a single expression with the static overload:

client = Regex.replace(attr.url, @"\.[a-z-./]+", "").Replace("formation-", "")