Develop Reference

Entity Framework Code First - Maintain a Long connection to Database

Below is my Code to Query a 24 Column database using linq
var list = (from x in db.graph_update
where x.serial == serial_number
&& (x.plotdate >= date_from && x.plotdate <= date_to)
select new {
x.plotdate,
x.Temperature
}).ToList();
Because the Database contains a large amounts to data, the connection time to grab all this data will take a long time and usually results in an error:
500 - The request timed out.
The web server failed to respond within the specified time.
How do I maintain this long running connection so it wouldn't timeout and be able to grab all of the data?

For whatever reason your query takes that long you can profile it and get max query time and just set timeout:
Entity Framework 6:
this.context.Database.CommandTimeout = 180;
Entity Framework 5:
((IObjectContextAdapter)this.context).ObjectContext.CommandTimeout = 180;

C# MongoDB.Driver : How to see if server is connected. GetServer Replacement

GetServer is gone for good. How do i check if the server is connected or even exists?
Example code:
// This server exists
var exists = new MongoClient("mongodb://192.168.2.109:27017");
// This server does not exist
var doesNotExist = new MongoClient("mongodb://194.168.200.129:27017");
// Both states return "Discennected"
var connStateExisting = exists.Cluster.Description.State;
var connStateNotExisting = doesNotExist.Cluster.Description.State;
// GetDatabase("name") works for both without errors.
How can i check if a server can be connected?

The Cluster.Description.State does not update immediately. When i checked, it was updated after roughly 100+ milliseconds. The driver contains a connection pool and it seems to do quite a lot asynchronous.
However, the Cluster-property has a "DescriptionChanged"-event that is fired once the connection is done.
If someone else has any knowledge about connections and timeouts, please share it.

Get MongoCluster Primary with C# Drver

I connect with the following code to a mongo database.
Then i iterated through the server descriptions of the cluster but the state is always "disconnected" but when i look with tools like monogchef i can see that all server are connected and there is one primary and all others are secondaries
var client = new MongoClient(conString);
var db = client.GetDatabase("admin");
foreach (var server in client.Cluster.Description.Servers)
{
Console.WriteLine(server.State); // Always returns disconnected.
}
How can I read who is the primary and when has been the last election?

Just found it.
Have to make a dummy request then i find the data under
server.ReplicaSetConfig.Primary

Serialize linq query so that it can be executed somewhere else

I am creating a client application that connects to a website in order to execute queries. I am not enabling the client to connect directly to the database but he can perform queries through the website.
The way I execute queries through the website is through linq. For example I may do:
MyEntities db = new MyEntities();
var customers = db.Customers.ToList();
Since the client does not have the connection string and sql server does not allow remote connections when he executes the above code it will obviously not work. My question is how can the client send that query to the web service?
The reason why I need this is because there are so many different types of queries and for each different one I have to create a different page. For example I have GetInvoices.aspx, GetCustomers.aspx, and I am always creating new ones just because I dont want the client to connect directly to the database. It will be nice if I could serialize the linq query and send that to the server. the server then should validate that I am not doing a delete statement for example and if thats the case then execute the query.
Eidt
This is what I am going to do for only select statements:
// Note connection string only have basics. It does not have password nor database.
public static string GenerateSelectQuery<T>(Func<Common.Data.TcEntities, IQueryable> method)
{
Common.Data.TcEntities db = new Common.Data.TcEntities(#"metadata=res://*/Data.Model1.csdl|res://*/Data.Model1.ssdl|res://*/Data.Model1.msl;provider=System.Data.SqlClient;provider connection string=""""");
var query = method(db);
return query.ToString();
}
then if I wish to create a custom query I will do:
var query = GenerateSelectQuery<Customer>(db => db.Customers.Where(x=>x.FirstName.Contains("a")));
I will send then that string to the server and expect an array of Customers. On the server side I will make sure string starts with select and it does not contain --.

Implementing a WCF Data Services, http client can query your data using the OData protocol.
For example, applying a select Name on your customers collections will be queryable using the http url:
http://youdomain/yourWCFDataServices.svc/Customers()?$select=Name

Multiple session-less requests to a page (which interacts with database) results in HTTP Error 500

I have an asp.net web page which interacts with a SQL Server database, grabs some data and then returns an XML response (which I feed into Freeswitch using xml_curl).
Because Freeswitch (FS from now on) does not store cookies, each request creates a new session.
When the number of requests gets too much (about 97 to 100), the SqlConnection.Open() method gets timeout from the SQL Server Instance, which then results in HTTP Error 500.
To test my assumption, I have created a small script using PHP and cURL, which make repeated requests to my asp.net page. If I store cookies (and thus sessions) in the PHP script I can make 10000 successful requests in almost 314 seconds.
But without sessions, I get stuck at about 97~100 requests, and then I get HTTP Error 500.
Is there anyway to overcome this problem?
==Edit==
Here is how I interact with the database:
String connectionString = WebConfigurationManager.ConnectionStrings["SqlServerConnection"].ConnectionString;
SqlConnection connection = new SqlConnection(connectionString);
SqlCommand command = connection.CreateCommand();
command.CommandType = CommandType.Text;
command.CommandText = "Select * from dbo.Template where Name = '" + name + "'";
Template template = new Template();
connection.Open();
SqlDataReader reader = command.ExecuteReader();
if (reader.HasRows)
{
reader.Read();
template.Name = reader["Name"].ToString();
template.XMLContent = reader["XMLContent"].ToString();
}
else
{
template.Name = "";
template.XMLContent = "";
}
reader.Close();
connection.Close();
return template;
And the Template table has these fields:
ID => int, identity, primary key
Name => nvarchar(255), unique
XMLContent => ntext

It appears you are using a connection pool. By default these pools have a max of 100 connections to your SQL server and queue any additional connections. The queue has a timeout (default 15 seconds) which can be extended if you wish to queue your requests longer. This means that you might get backed up on your server. You can also increase the pool max size if your SQL server can handle it.
Here is how you increase your connection settings by adding these parameters:
Timeout=60
Max Pool Size=150
etc etc

Some steps to impove this code.
If you do not need session, disabled it for this page so not cookie is going to be made.
Use some cache here base on the name If the request for name is the same, get it from cache and not open the database
Use a static variable to read only one time the connection string.
Place it on [try catch | using] , to be sure that you close the connection in case of failure
Maybe you can try a mutex lock logic, to avoid too many request together.
Use parameters on your sql call.

In addition to #Aristos suggestions:
Use Async-Pages!
Example and "Benchmark"
Some time ago I asked nearly the same question here on so