Mehfuz's WebLog : OpenLinqToSql

Article of the day at Asp.net

mehfuzh — Tue, 22 Jan 2008 06:41:00 GMT

My Creating custom LINQ provider using LinqExtender is article of the day at asp.net. Those of you haven't check that out yet, I would suggest to have a look, it shows the easiest way of creating LINQ providers without any Expression parsing knowledge.

Have Fun!!

[New Article] Creating custom LINQ provider using LinqExtender

mehfuzh — Mon, 07 Jan 2008 23:32:39 GMT

First of all happy new year, secondly my new article is just published at Dotnetslackers. This explains the detail of creating custom LINQ providers using Linqextender.

You can check that out at http://dotnetslackers.com/articles/csharp/CreatingCustomLINQProviderUsingLinqExtender.aspx

Moreover, I would like to add some tiny enhancements to the extender.

1. All the extender descendant can now do something like.

var query = (from q in _queryContext
             orderby q.LastUpdated descending
             select new { q.Id, q.Title, q.LastUpdated }).Take(1);
 
int count = query.Count();

2. OpenLinqToSql, which is a part of Linqextender, now, supports SQLCE database.

3. Easy OnError event for exception trapping.

In the end, there are plenty of things that needs to done and to be told, but the article explains exactly how to get started and create a provider in no time. Please take a look , and if possible give some votes.

LinqExtender 1.2 is out now

mehfuzh — Mon, 24 Dec 2007 20:31:25 GMT

Since, the first release of LinqExtender, I found quite a bit download and feedback from community around. I did plenty of changes and tried to make it as simple as possible for creating custom providers, without knowing a bit of reflection and expression parsing of the core framework.

After the release , I was asked by people around , why do we need Linq , when we can do it by method calls, the answer is, Linq gives another level of abstraction to method call that enables you to set a query domain for developers, by means of strongly type query objects, it's not like exposing the data access layer to the front end developer, but it is like giving them a playground with proper boundary. In other words, front end developers now can query on some specific criteria that we set by means of query object , still giving them a flexibility of functional programming.

Now on to the release 1.2. it has come with query info retrieval wrapper and some new features ,which could be useful while making custom providers.

I have mentioned in following post, how query data is delegated to Process routine, that will be overridden in the custom provider that developer is working on.

http://weblogs.asp.net/mehfuzh/archive/2007/12/02/linqextender.aspx

Now with new release it looks something like

protected override void Process(LinqExtender.Interface.IModify<T> items, Bucket bucket)

As , you can see that it has Bucket object, which is nothing but a wrapper for holding the query details. Each Bucket has some BucketItem. BucketItem contains info for each property used in the expression separated by &&.

Typically BucketItem looks like

BucketItem
Name - Property name, different if the used with OriginalFieldNameAttribute, or less it is same as property name.
Value - value in the query , for which the property is compared. Default value, Null.
Unique - True , if UniqueIdentifierAttribute or its inherited type is used on property.Here, one can Use UniqueIdentifierAttribute directly on property or can use any inherited form like, PrimaryKeyAttribute that inherits the UniqueIdentifierattribute, to reflect value to this property.
RelationType : Enum - Equal , LessThan, LessThatEqual, GreaterThan, GreaterThanEqual. Used to identify which type of logical comparison is used.

Any of the property, which is not used in a query , BucketItem.Value and BucketItem.RelationType will have the default value for it, which is Null and Equal respectively.

Now, Going Back to Bucket, it looks like

Bucket
IDictionary<string, BucketItem> Items - List of items for property, where string is the property name of the query object, BuckItem represents how the Property is treated and used in query.
ItemsToTake - default null , if Take is not specified in query.
ItemsToTake - default 0, if Skip is not specified in query.
UniqueItems - string[], contains the name of property on which UniqueIdentifierAttribute or its derivative is applied.

As, we can see from this release that Linqextender supports most common logical expression rather than just Equal expression.

The new release also supports "New Type" queries, which i already mentioned in this post

http://weblogs.asp.net/mehfuzh/archive/2007/12/16/anonymous-type-in-linqextender.aspx

Finally, I have added CTE(Common table expression) generation for OpenLinqToSql (Formerly known as TinyLinqToSql) provider.

Now , queries like the following with Take and Skip

SqlQuery<Book> context = new SqlQuery<Book>();

var query = (from q in _queryContext
             orderby q.LastUpdated ascending
             select q).Take(5).Skip(2);

// this is where the query will execute
foreach(var book in query)
{
 // do something useful 
}

Will generate Sql like...

WITH FilteredList(Id,Author,Title,ISBN,LastUpdated, [RowNumber]) AS(
SELECT Id,Author,Title,ISBN,LastUpdated, Row_number()OVER(ORDER BY 
LastUpdated asc) as [RowNumber] FROM Book 
)Select * from FilteredList WHERE [Rownumber] Between (3) and (7)

Here, Take(5), Skip(2), it will take 5 items starting from 3.

For more, I would suggest to have a look at release page of LinqExtender

OpenLinqToSql provider is made to exercise the LinqExtender engine , it is provided with the LinqExtender source and with NUnit test class in LinqExtender project itself. There is another project named Linq.Flickr, where I have originally started working on with Linq provider and then made LinqExtender, this is currently a separate project. This shows another possible implementation of LinqExtender, for service end points.

Happy Holidays!!!

LinqExtender 1.01 released

mehfuzh — Mon, 10 Dec 2007 15:41:00 GMT

I have released the new version of LinqExtender, it now support orderby queries

Like I can easily do

var query = from q in context
            where q.Id == 1
            orderby q.Id descending
            select q;

Also, I have uploaded a tiny linq to sql project named OpenLinqToSql which is built on LinqExtender and can be downloaded from LinqExtender release page

To start working with OpenLinqToSql, all is needed.

First create a object that represents the entity class.For example , i have created a Book table in database , which looks like

CREATE TABLE [dbo].[Book](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [Author] [nvarchar](255) NOT NULL,
    [Title] [nvarchar](255) NOT NULL,
    [ISBN] [nvarchar](50) NOT NULL,
    [LastUpdated] datetime NOT NULL

)

For which the representation of object is

class Book : QueryObjectBase
    {
        [LinqVisible, Identity]
        public int? Id { get; set; }
        [LinqVisible]
        public string Author { get; set; }
        [LinqVisible]
        public string Title { get; set; }
        [LinqVisible]
        public string ISBN { get; set; }
        [LinqVisible]
        public DateTime? LastUpdated {get; set;} 

        public override bool IsNew
        {
            get
            {
                return Id == null;
            }
        }
    }

Here to note that, in order to use a property in query expression, LinqVisibleattribute is used. Also, Non string properties, should be made Nullable.

Finally, I can do the following to get things going

SqlQuery<Book> context = new SqlQuery<Book>();

Write the query.

var query = from q in context
            orderby q.Id descending
            select q;

The OpenLinqToSql can talk with SQLCE databases as well. Also, this is just an tiny project that helps to understand how to make providers using LinqExtender, but for real flavor , use the LinqToSql that comes with .net 3.5

Thanks