I am little new to linq and was wondering how i can select the application in the following xml based on the application name using Extension Methods (not using the query expression)
<applicationlist>
<application>
<name>test1</name>
<ele1>852</ele1
<ele2>http://localhost/test1</ele2>
</application>
<application>
<name>test2</name>
<ele1>456</ele1
<ele2>http://localhost/test2</ele2>
</application>
</applicationlist>
Assuming that by "the SQL way of selecting" you mean "using a query expression", let's start off with your query expression:
var v = from b in root.Descendants("application")
where b.Element("name").Value.Trim().ToLower() == appName.Trim().ToLower()
select b;
With extension methods, this would just be:
var v = root.Descendants("application")
.Where(b => b.Element("name").Value.Trim().ToLower() ==
appName.Trim().ToLower());
I would recommend against making case-insensitive comparisons this way though - it has cultural problems. Use something like this instead:
var v = root.Descendants("application")
.Where(b => b.Element("name").Value.Trim().Equals(appName.Trim(),
StringComparison.CurrentCultureIgnoreCase);
(or one of the other StringComparison options - or an instance of StringComparer).
You might also want to trim appName once rather than for every comparison...
Related
Is there an Xpath to find a cousin node that has an element that matches the value of an element in the current node?
Please see below - I am iterating over each "Order" node and want to return the value of LocationID from the Collection node that has the same OrderLoadRef value as the order. For the first order it should return "AAA", for the second it should return "BBB".
The XPath works if I change the value of the OrderLoadRef manually, but how to I set it to be the value of the OrderLoadRef in the current Order Element? I've tried using the self axis, but think by the time we get to the condition, "self" is the collection node, not the order?
I can't hard code relative collection / order node positions as there could be a variable number of these nodes in the XML that my parser receives.
XDocument xDoc = XDocument.Parse(#"<DocRoot>
<Load>
<Collections>
<Collection>
<OrderLoadRef>1</OrderLoadRef>
<LocationID>AAA</LocationID>
</Collection>
<Collection>
<OrderLoadRef>2</OrderLoadRef>
<LocationID>BBB</LocationID>
</Collection>
</Collections>
<Orders>
<Order>
<OrderRef>1521505</OrderRef>
<OrderLoadRef>1</OrderLoadRef>
</Order>
<Order>
<OrderRef>1521505_2</OrderRef>
<OrderLoadRef>2</OrderLoadRef>
</Order>
</Orders>
</Load>
</DocRoot>");
List<XElement> orders = xDoc.XPathSelectElements("//Order").ToList();
foreach(XElement order in orders)
{
string locationId = order.XPathSelectElement("parent::Orders/parent::Load/Collections/Collection[OrderLoadRef = {OrderLoadRef from current order element}]/LocationID").Value;
}
Edited to add: I need this to be a purely XPath solution as I'm not able to alter the C# code in the parser. More than happy to be told it's not possible, but wanted to make sure before I relayed the message!
As Mads said, XPath 3 and later (i.e. the current version 3.1) allows you to use a let expression so e.g.
for $order in /DocRoot/Load/Orders/Order
return
let $col := /DocRoot/Load/Collections/Collection[OrderLoadRef = $order/OrderLoadRef]/LocationID
return $col
is pure XPath 3 and returns (for your sample) the two LocationID elements:
<LocationID>AAA</LocationID>
<LocationID>BBB</LocationID>
In the .NET framework XmlPrime and Saxon.NET support XPath 3.1 and XQuery 3.1 although only XmlPrime has extension methods for C# to work against XDocument, I think, Saxon.NET does allow XPath 3.1 against its XDM tree model or against System.Xml.XmlDocument.
XPath 3.0 (and greater) supports let expressions, which would allow you to do what you want. You could let a variable with the OrderLoadRef from the context node and use it within a predicate selecting the desired Collection by it's OrderLoadRef.
For a static XPath 1.0 expression, I don't think you can achieve what you want. You would need to construct the XPath using the context node information.
Inside your for loop, create a variable for the Order's OrderLoadRef value. Use that value to construct the XPath that you want to evaluate to then select the locationId
foreach(XElement order in orders)
{
string orderLoadRef = order.XPathSelectElement("OrderLoadRef").Value;
string locationId = order.XPathSelectElement("ancestor::Load/Collections/Collection[OrderLoadRef = " + orderLoadRef + "]/LocationID").Value;
//do something with the locationId
}
I have a class with a local variable called "group", as you can see I give it a value in the constructor (the value I assign it is null if it matters):
The strange thing is, when I debug my project, the name "group" suddenly becomes "#group":
I don't have this for any other variables, is this something of Visual Studio 2015? Never saw this before in earlier versions. If it's not a bug, what does it mean?
Edit: "#group" and "group" can both be used in code:
The word "group" is a keyword, as used in LINQ:
var x = from y in collection
group y by p.name into g ....
In C# keywords can be uses as names, if they are prefixed by # and used like this:
var #class = "car";
I have the following code that's repeated:
var ccaNumber = (from r in xDoc.Elements("ResultSet").Elements("DataRow")
where Convert.ToInt32(r.Element("PaymentPlanNumber").Value) == payPlan.OrderNumber
Ideally, I want to create the above as an expression then add my clause to the end of it.
So, I created the expression as follows:
Expression currExp = from r in xDoc.Elements("ResultSet").Elements("DataRow")
where Convert.ToInt32(r.Element("PaymentPlanNumber").Value) == payPlan.OrderNumber;
I now want to combine them:
var ccaNumber = (currExp select r.Element("CreditCardAuthorityNumber").Value).FirstOrDefault();
However I now get the following error:
Invalid expression term ')'
Any suggestions?
ta,
yogi
I think you are mixing things up here.
What you can do is:
var items = from r in xDoc.Elements("ResultSet").Elements("DataRow")
where Convert.ToInt32(r.Element("PaymentPlanNumber").Value) == payPlan.OrderNumber
select r;
This declares items as a Enumerable of elements that match your Where-Condition.
And then you can use those defined items like this:
var ccaNumber = items.Select(item=>item.Element("CreditCardAuthorityNumber").Value).FirstOrDefault();
However, this is all utilising lazy evaluation and you need to take care of multiple enumerations here. Here is a pretty indepth explanaition that is way better than my sh*tty english.
When adding to an existing expression, you need to use the lambda syntax, not the Linq syntax:.
Try:
var ccaNumber = (currExp
.Select(r=>r.Element("CreditCardAuthorityNumber").Value))
.FirstOrDefault();
Probably really easy but im having trouble finding documentation online about this
I have two activerecord queries in Ruby that i want to join together via an OR operator
#pro = Project.where(:manager_user_id => current_user.id )
#proa = Project.where(:account_manager => current_user.id)
im new to ruby but tried this myself using ||
#pro = Project.where(:manager_user_id => current_user.id || :account_manager => current_user.id)
this didnt work, So 1. id like to know how to actually do this in Ruby and 2. if that person can also give me a heads up on the boolean syntax in a ruby statement like this altogether.
e.g. AND,OR,XOR...
You can't use the Hash syntax in this case.
Project.where("manager_user_id = ? OR account_manager = ?", current_user.id, current_user.id)
You should take a look at the API documentation and follow conventions, too. In this case for the code that you might send to the where method.
This should work:
#projects = Project.where("manager_user_id = '#{current_user.id}' or account_manager_id = '#{current_user.id}'")
This should be safe since I'm assuming current_user's id value comes from your own app and not from an external source such as form submissions. If you are using form submitted data that you intent to use in your queries you should use placeholders so that Rails creates properly escaped SQL.
# with placeholders
#projects = Project.where(["manager_user_id = ? or account_manager_id = ?", some_value_from_form1, some_value_from_form_2])
When you pass multiple parameters to the where method (the example with placeholders), the first parameter will be treated by Rails as a template for the SQL. The remaining elements in the array will be replaced at runtime by the number of placeholders (?) you use in the first element, which is the template.
Metawhere can do OR operations, plus a lot of other nifty things.
I'm trying to find the correct names for these 2 "types" of coding expressions in LINQ so that I can refer to them correctly. I want to say that the first is called "Fluent Style"?
var selectVar = arrayVar.Select( (a,i) => new { Line = a });
var selectVar =
from s in arrayVar
select new { Line = s };
First - calling an extension method.
This style of coding is called "fluent interface" as you mentioned.
Second method is called language integrated query
The name of the second form is "query comprehesion syntax", which the compiler translates into the first form.
The first isn't even really LINQ, it's a lambda expression, with a type invariant object created.
(a) => new { blah = b}
The second is a LINQ query filling an on the fly class that has a property Line.
There is no hashrocket operator in this one, so this one is just plain old linq.