Language Integrated Query (LINQ) is a cool feature of .NET languages like C# that allows you to perform SQL-like query right within the language against language’s data structures (lists, arrays etc.) But one drawback of LINQ – you have to know in advance, at compile time which fields to select, what filter conditions would be. Sometimes there’s a need to supply these at runtime – e.g. user selects which fields they want to see
Thankfully there exists Dynamic LINQ Library that allows you to supply LINQ parameters as a string akin Dynamic SQL. Here’s an example of such query from the library’s homepage:
var query = db.Customers
.Where("City == @0 and Orders.Count >= @1", "London", 10)
.OrderBy("CompanyName")
.Select("new(CompanyName as Name, Phone)");
Now, one thing that LINQ can do is query XML. So in theory if we load, say, this XML:
<DATA_CENTER>
<SERVER IP="1.2.3.4">
<OS>Windows</OS>
</SERVER>
<SERVER IP="5.6.7.8">
<OS>Linux</OS>
</SERVER>
</DATA_CENTER>
into an XElement and run something like this
var query0 = myXElement.Elements()
.AsQueryable()
.Select("new (Attribute(\"IP\").Value as IP, Element(\"OS\").Value as OS)")
it would produce list of IPs and OSes. Unfortunately this doesn’t work. Continue reading →
