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Posts tagged LINQ Query
LINQ wonder world
Feb 5th
I am sure that, if you are a developer, at some point in your career heard about and asked yourself: what is LINQ? If not, there’s no problem, you’ll find out now : LINQ comes from language-integrated query and it is a collection of extensions to the .NET Framework that encompass language-integrated query, set, and transform operations. It helps developers by extending both C# and Visual Basic, adding native querying capabilities to these languages. It also comes with class libraries to get the full advantage out of these capabilities.
As we discussed in my previous article, Import CSV file and query it with LINQ, we are able to load and parse the file into a IQuerable collection, thus giving us the oportunity to do more and more SQL- like operations on it.
The C# 3.0 specification defines a so-called Query Expression Pattern along with translation rules from a LINQ expression to an expression in a subset of C# 3.0 without LINQ expressions. The translation thus defined is actually un-typed, which, in addition to lambda expressions being interpretable as either delegates or expression trees, allows for a great degree of flexibility for libraries wishing to expose parts of their interface as LINQ expression clauses. For example, LINQ to objects works on IEnumerable<T>s and with delegates, whereas LINQ to SQL makes use of the expression trees.
Import CSV file and query it with LINQ
Feb 4th
Assume that you have an plain text, old Comma Separated Values file filled with your precious export from a legacy system. How can you process it easily now? The first answer that comes to mind is to parse it and load it into a datatable and later process it by using DataTable.Select() method. But this approach has some limitations – like splitting data into several tables and then join them.
One would imagine that parsing CSV files is a straightforward and boring task, given that it is quite a while since CSV is around. Some of them are correct – in the sense that many implementations merely use some splitting method like String.Split(). Some don’t even offer the specification of the values splitting character – so your file wouldn’t be parsed correctly if instead of , you have ; as separator – yet another thing to modify if you’re lucky enough to have the sources. Others will not handle properly field values with commas because the simple split method of the String class. But there are better implementations that take care about escaped quotes, trimming spaces before and after fields and other small and useful details, but very few that I found did it all as I liked it – and at least as importantly, in a fast and efficient manner.
