Skip to main content

C# Learning: LINQ to SQL(First Example)


The first step in building a LINQ to SQL application is declaring the classes we’ll
use to represent your application data: our entities.


[Table(Name="Contacts")]
class Contact
{
[Column(IsPrimaryKey=true)]
public int ContactID { get; set; }
[Column(Name="ContactName"]
public string Name { get; set; }
[Column]
public string City { get; set; }
}


The next thing we need to prepare before being able to use language-integrated
queries is a System.Data.Linq.DataContext object. The purpose of DataContext

is to translate requests for objects into SQL queries made against the database and
then assemble objects out of the results.

The full example below,

using System;
using System.Linq;
using System.Data.Linq;
using System.Data.Linq.Mapping;
static class HelloLinqToSql

{

static void Main()
{
string path =
System.IO.Path.GetFullPath(@"..\..\..\..\Data\northwnd.mdf");
DataContext db = new DataContext(path);



var contacts =
from contact in db.GetTable<Contact>()
where contact.City == "Paris"
select contact;

foreach (var contact in contacts)
Console.WriteLine("Bonjour "+contact.Name);
}
}


Notice how easy it is to get strongly typed access to a database thanks to LINQ.
This is a simplistic example, but it gives you a good idea of what LINQ to SQL has
to offer and how it could change the way you work with databases.
Let’s sum up what has been done automatically for us by LINQ to SQL:
■ Opening a connection to the database
■ Generating the SQL query
■ Executing the SQL query against the database
■ Creating and filling our objects out of the tabular results


You’ll notice the following things in the old-school
code when comparing it with our LINQ to SQL code:
■ Queries explicitly written SQL in quotes
■ No compile-time checks
■ Loosely bound parameters
■ Loosely typed result sets
■ More code required
■ More knowledge required





Comments

Popular posts from this blog

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold highlighted in example below) which resolve the problems.   example:
<band height="20" splitType="Stretch"> <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/> …

JasperReports - Configuration Reference

Live - solving the jasper report out of memory and high cpu usage problems

I still can not find the solution. So I summary all the things and tell my boss about it. If any one knows the solution, please let me know.


Symptom: 1.The JVM became Out of memory when creating big consumption report 2.Those JRTemplateElement-instances is still there occupied even if I logged out the system
Reason:         1. There is a large number of JRTemplateElement-instances cached in the memory 2.The clearobjects() method in ReportThread class has not been triggered when logging out
Action I tried:      About the Virtualizer: 1.Replacing the JRSwapFileVirtualizer with JRFileVirtualizer 2.Not use any FileVirtualizer for cache the report in the hard disk Result: The japserreport still creating the a large number of JRTemplateElement-instances in the memory     About the work around below,      I tried: item 3(in below work around list) – result: it helps to reduce  the size of the JRTemplateElement Object                Item 4,5 – result : it helps a lot to reduce the number of  JRTemplateE…