ASP.NET - LINQ

LINQ which I think is one of the most exciting features in Orcas. LINQ makes the concept of querying a first-class programming concept in .NET. The data to be queried can take the form of XML (LINQ to XML), databases (LINQ-enabled ADO.NET: LINQ to SQL, LINQ to Dataset and LINQ to Entities) and objects (LINQ to Objects). LINQ is also highly extensible and allows you to build custom LINQ enabled data providers (e.g.: LINQ to Amazon, LINQ to NHibernate, LINQ to LDAP).

I will discuss some of the new language features and improvements that are introduced in C# 3.0, and it is those features that enable the full power of LINQ which makes it possible to write something like this:

LINQ is a uniform programming model for any kind of data access. LINQ enables you to query and manipulate data independently of data sources. Below figure 'LINQ' shows how .NET language stands over LINQ programming model and works in a uniformed manner over any kind of data source. It’s like a query language which can query any data source and any transform. LINQ also provides full type safety and compile time checking.
LINQ can serve as a good entity for middle tier. So it will sit in between the UI and data access layer.
 

Figure - LINQ

Below is a simple sample of LINQ. We have a collection of data ‘objcountries’ to which LINQ will is making a query with country name ‘India’. The collection ‘objcountries’ can be any data source dataset, datareader, XML etc. Below figure ‘LINQ code snippet’ shows how the ‘ObjCountries’ can be any can of data. We then query for the ‘CountryCode’ and loop through the same.

Figure: - LINQ code snippet

How does LINQ help us from the perspective of business objects?
 

One of the tedious jobs in business object is parsing and searching object collections. For instance consider the below figure where we want to search a country by an ‘ID’ value. So what we do is loop through the collection and get the object. Many may argue how about keeping a key in List or Array. The below example is just a sample. For instance if you want to search using country code and name, list / collection keys will not work with those multi-value searches.
 

In other words using LINQ we can query business object collections and filter the collection in a single LINQ query.

1. LINQ syntax beats SQL syntax. SQL is flawed in that queries become exponentially difficult to write as their complexity grows. LINQ scales much better in this regard. Once you get used to it, it's hard to go back.
2. Database queries are easily composable. You can conditionally add an ORDER BY or WHERE predicate without discovering at run-time that a certain string combination generates a syntax error.
3. More bugs are picked up at compile-time.
4. Parameterization is automatic and type-safe.
5. LINQ queries can directly populate an object hierarchy.
6. LINQ to SQL provides a model for provider independence that might really work.
7. LINQ significantly cuts plumbing code and clutter. Without sweeping stuff under the carpet, like Workflow or Datasets. This is a credit to the design team.
8. C# hasn't suffered in the process (in fact, it's gained).