Is there an equivalent to the F# TypeProvider in C#? I am looking at the easiest way to read an Xml file with C#. At this point I am planning to use XDocument, but I was wondering if there was something better.
F# makes it so easy to read an Xml file that I wonder if I shouldn't switch language for Xml processing!
As already mentioned, C# does not support type providers and there is no easy way for emulating them (as Gustavo mentioned, you could use generated type providers through a small F# library, but XML, JSON, CSV and others are not this kind.)
I think using F# library that does the processing is the best approach.
A more complicated alternative would be to write code that lets you define types to model the XML file in C# and then automatically reads the file into these classes. I do not think anything like this exists, but I wrote a similar thing in F# (before type providers), so you can see the snippet for inspiration. The usage looks like this:
// Modelling RSS feeds - the following types define the structure of the
// expected XML file. The StructuralXml parser can automatically read
// XML file into a structure formed by these types.
type Title = Title of string
type Link = Link of string
type Description = Description of string
type Item = Item of Title * Link * Description
type Channel = Channel of Title * Link * Description * list<Item>
type Rss = Rss of Channel
// Load data and specify that names in XML are all lowercase
let url = "http://feeds.guardian.co.uk/theguardian/world/rss"
let doc : StructuralXml<Rss> =
StructuralXml.Load(url, LowerCase = true)
// Match the data against a type modeling the RSS feed structure
let (Rss(channel)) = doc.Root
let (Channel(_, _, _, items)) = channel
for (Item(Title t, _, _)) in items do
printfn "%s" t
Is there any reason why you can't add an F# library to your solution? That project can create the abstraction over the XML that you want, and you could consume it from your C# projects.
No, it's not possible to use type providers directly in C#.
For generated type providers, you can "instantiate" the type provider in a F# project, and then use that from C#, but that doesn't work for erased type providers like CsvProvider, JsonProvider, XmlProvider, Freebase or Worldbank. (It will work for the builtin SqlProvider and WsdlProvider, though).
There has been some discussion of switching CsvProvider, JsonProvider and XmlProvider to the generated model so they're usable for data-binding in C# (https://github.com/fsharp/FSharp.Data/issues/134#issuecomment-20104995), but that will probably take a while to happen.
My suggestion is to either swtich to F# altogether, or create record types that mirror the types that the type provider creates. Example:
type T = {
A : int
B : string
(...)
}
type XmlT = XmlProvider<"xml file">
let getXml() =
let xml = XmlT.GetSample()
{ A = xml.A
B = xml.B
(...) }
I took a look at your link to the XmlProvider in F# and I have not seen anything like it in C#. I use C# with Xml quite alot and often use XDocument and XElement to load and parse Xml with. Once I have Xml loaded into the XDocument I use Linq to Xml to perform similar things. I often use Linq Pad for general queries into the Xml which works well with C# not sure about F# though.
Related
First I load the file in a structure
XElement xTree = XElement.Load(xml_file);
Then I create an enumerable collection of the elements.
IEnumerable<XElement> elements = xTree.Elements();
And iterate elements
foreach (XElement el in elements)
{
}
The problem is - when I fail to parse the element (a user made a typo or inserted a wrong value) - how can I report exact line in the file?
Is there any way to tie an element to its corresponding line in the file?
One way to do it (although not a proper one) –
When you find a wrong value, add an invalid char (e.g. ‘<’) to it.
So instead of: <ExeMode>Bla bla bla</ExeMode>
You’ll have: <ExeMode><Bla bla bla</ExeMode>
Then load the XML again with try / catch (System.Xml.XmlException ex).
This XmlException has LineNumber and LinePosition.
If there is a limited set of acceptable values, I believe XML Schemas have the concept of an enumerated type -- so write a schema for the file and have the parser validate against that. Assuming the parser you're using supports Schemas, which most should by now.
I haven't looked at DTDs in decades, but they may have the same kind of capability.
Otherwise, you would have to consider this semantic checking rather than syntactic checking, and that makes it your application's responsibility. If you are using a SAX parser and interpreting the data as you go, you may be able to get the line number; check your parser's features.
Otherwise the best answer I've found is to report the problem using an xpath to the affected node/token rather than a line number. You may be able to find a canned solution for that, either as a routine to run against a DOM tree or as a state machine you can run alongside your SAX code to track the path as you go.
(All the "maybe"s are because I haven't looked at what's currently available in a very long time, and because I'm trying to give an answer that is valid for all languages and parser implementations. This should still get you pointed in some useful directions.)
I have two applications. One application saves options and configurations down as JSON and the other reads the JSON and performs it's task based on the fields in the JSON. Now I want to filter a list that is in application-2. How can I pass how I want the list to be filtered into a string to be stored in JSON and then reinterpreted by application-2?
Is there anyway to serialize linq/lambda expressions and deserialize them? Or is there a better approach like creating a class that contains some filterable options like equal-to, not-equal-to, greater-than, less-than, contains, etc?
Unfortunately there is no way to serialize and serialize a lamda expression in c#, because it is make in compile time.
The Lamda after the compilation generates a function and the compiler call this function when the lamda expression is used.
You have one option, but is not easy :) Yoy have to store a c# code in json file, and the application-2 will read it, parse it, compile it, and execute it.
But itt will be a complete assembly (like one class) not only one lamdba expression.
If you use :net framrwork here is an example:
https://www.codeproject.com/Tips/715891/Compiling-Csharp-Code-at-Runtime
If you use .Net Core, teh ypu have to use roslyn: https://josephwoodward.co.uk/2016/12/in-memory-c-sharp-compilation-using-roslyn
I hope it helps
regrads
I found for another solution for this problem. You can store and revert an Expression from string! :)
The only need, the two module (or two program in your case) must be the known the same type.
Sample code:
var discountFilter = "album => album.Quantity > 0";
var options = ScriptOptions.Default.AddReferences(typeof(Album).Assembly);
Func<Album, bool> discountFilterExpression =
await CSharpScript.EvaluateAsync<Func<Album, bool>>(discountFilter, options);
var discountedAlbums = albums.Where(discountFilterExpression);
Regrads
gy
If you want to filter javascript arrays in pure JSON, you can use Jpath and Json.Net
For example:
var token = JToken.Parse("json string here")
var tokens = token.SelectTokens("$.YourJsonArray[?(#.Property == something)]")
I am trying to parse a file in MVC C#, see the format below. Since its not in JSON I cannot use the Javascript serializer to deserialize to an object. The other option is use to LINQ and read line by line and retrieve the desired values. Could any one recommend a more efficient way to do it.
The first field I need to retrieve is the ASSAY NUMBER (for example value 877) from ASSAYS
and then the ASSAY_STATUS field from TEST_REPLICATE which could be multiple nodes. Thanks
LOAD_HEADER
{
EXPERIMENT_FILE_NAME "xyz.json"
EXPERIMENT_START_DATE_TIME 05.21.2012 03:44:01
OPERATOR_ID "Q_SI"
}
ASSAYS
{
ASSAY_NUMBER 877
ASSAY_VERSION 4
ASSAY_CALIBRATION_VERSION 1
}
TEST_REPLICATE
{
REPLICATE_ID 1985
ASSAY_NUMBER 877
ASSAY_VERSION 4
ASSAY_STATUS Research
}
TEST_REPLICATE
{
REPLICATE_ID 1985
ASSAY_NUMBER 877
ASSAY_VERSION 4
ASSAY_STATUS Research
}
You could either hack something together or use a parser generator like ANTLR or Coco/R. Both can generate parsers in C#.
I'm more fond of using a parser-combinator (a tool for constructing parsers using parser building blocks) than parser generators. I've had passable experience with Piglet, which is written with/for C#, and is pretty easy to use, and amazing experience with FParsec, but it's written for F#.
As far as parser generators go, there are those suggested by stmax, and there is also TinyPG, which a member recommended me once.
You can also roll your own parser. I suggest basing it on some sort of state machine model, though in this simple case, like Kirk Woll suggested, you could probably get by with some plain old string manipulation.
I think the answer to this hinges upon whether or not there will ever be more than one ASSAY_NUMBER value in the file. If so, the easiest and surest way I know is to read the file line-by-line and get the data you desire.
If, however, you know that each file is unique to a specific ASSY_NUMBER, you have a much simpler answer: read the file as one string and use REGEX to pull out the information you desire. I am not an expert on REGEX, but there are enough examples online that you should be able to create one that works.
The answer to this question shows how to load a Json string to a hard-coded class using JavaScriptSerializer. However, the class structure has to be coded, and this looks impractical if you're just interested in a few values, and not interested in parsing the whole string.
Is there something similar to XElement, where I can simply load a XML string and then use xElement.Elements("Items").Select( el => el.Elements("Title")) in order to list the title of all items, for example. I prefer if I can use pure .NET without third-party libraries. It would be nice if I can also linq it like XElement
In case the context is useful, I'm trying to parse the a list of question provided by StackExchange API (json format) to a nicely formatted string, and I only want some infos like title, link, and author.
It sounds like what you are really asking for is a Linq to JSON adapter. Why be burdened by XML if you don't need to be? JSON is an object serialization format, not an XML format, so you should think of it as "How can I use LINQ to Objects with objects from JSON?
A quick google search for "Linq json" turns up several interesting topics. Give it a spin.
Is it possible to use variables like <%=person.LastName %> in XML string this way?
XElement letters = new XElement("Letters");
XElement xperson = XElement.Parse("<Table><Row><Cell><Text>
<Segment>Dear <%=person.Title%> <%=person.FirstName%> <%=person.LastName%>,
</Segment></Text></Cell></Row>...");
foreach (Person person in persons){
letters.Add(xperson)
}
If it's possible, it would be a lifesaver since I can't use XElement and XAttribute to add the nodes manually. We have multiple templates and they frequently change (edit on the fly).
If this is not doable, can you think of another way so that I can use templates for the XML?
Look like it's possible in VB
http://aspalliance.com/1534_Easy_SQL_to_XML_with_LINQ_and_Visual_Basic_2008.6
This is an exclusive VB.NET feature known as XML Literals. It was added in VB 9.0. C# does not currently support this feature. Although Microsoft has stated its intent to bridge the gap between the languages in the future, it's not clear whether this feature will make it to C# any time soon.
Your example doesn't seem clear to me. You would want to have the foreach loop before parsing the actual XML since the values are bound to the current Person object. For example, here's a VB example of XML literals:
Dim xml = <numbers>
<%= From i In Enumerable.Range(1, 5)
Select <number><%= i %></number>
%>
</numbers>
For Each e In xml.Elements()
Console.WriteLine(e.Value)
Next
The above snippet builds the following XML:
<numbers>
<number>1</number>
<number>2</number>
<number>3</number>
</numbers>
Then it writes 1, 2, 3 to the console.
If you can't modify your C# code to build the XML dynamically then perhaps you could write code that traverses the XML template and searches for predetermined fields in attributes and elements then sets the values as needed. This means you would have to iterate over all the attributes and elements in each node and have some switch statement that checks for the template field name. If you encounter a template field and you are currently iterating attributes you would set it the way attributes are set, whereas if you were iterating elements you would set it the way elements are set. This is likely not the most efficient approach but is one solution.
The simplest solution would be to use VB.NET. You can always develop it as a stand-alone project, add a reference to the dll from the C# project, pass data to the VB.NET class and have it return the final XML.
EDIT: to clarify, using VB.NET doesn't bypass the need to update the template. It allows you to specify the layout easier as an XML literal. So code still needs to be updated in VB once the layout changes. You can't load an XML template from a text file and expect the fields to be bound that way. For a truly dynamic solution that allows you to write the code once and read different templates my first suggestion is more appropriate.