I am using saxon to process my xpath, but sometimes xml file comes with namespace declaration which make my class to throw exception.
Is there any way to ignore namespace while using saxon as we do with dom i.e
builder.setEntityResolver(new EntityResolver()
{
public InputSource resolveEntity(String publicId,
String systemId) throws SAXException,IOException
{
return null;
}
});
If you do not want to use namespaces in your XPath, you can use local-name(), for example:
/pref:root/pref:element1[#attr="value"]/pref:element2
If you have the above XPath (with namespaces) you can also write is as this:
/*[local-name() = "root"]/*[local-name() = "element1"][#attr="value"]/*[local-name() = "element2"]
This will allow you not to use namespaces
Related
Using Saxon HE 9.6 as a JAXP implementation
Have an HTML document with the XHTML namespace
//*:title returns the expected value, but //title doesn't
I'd really like to just use //title. How can this be done?
Alternatively, can I just remove a namespace from an already constructed Document?
See https://saxonica.plan.io/boards/3/topics/1649, you can cast the JAXP XPath object you have created from a Saxon XPathFactory implementation to a net.sf.saxon.xpath.XPathEvaluator and then set the default XPath namespace for XPath evaluation with e.g.
((XPathEvaluator)xpath).getStaticContext().setDefaultElementNamespace("http://www.w3.org/1999/xhtml");
Then a path //title will select title elements in the XHTML namespace. I tested that to work in a sample
XPathFactory xpathFactory = new XPathFactoryImpl();
XPath xpath = xpathFactory.newXPath();
((XPathEvaluator)xpath).getStaticContext().setDefaultElementNamespace("http://www.w3.org/1999/xhtml");
String xhtmlSample = "<html xmlns='http://www.w3.org/1999/xhtml'><head><title>This is a test</title></head><body><h1>Test</h1></body></html>";
InputSource source = new InputSource(new StringReader(xhtmlSample));
System.out.println("Found: " + xpath.evaluate("//title", source));
Inspired by this post dynamic-repositories-in-lightspeed I am trying to build my own like this.
I have a abstract GenericRepository like this. I have omitted most of the code for simplicity (Its just normal Add/Update/Filtering methods).
public abstract class GenericRepository<TEntity, TContext> :
DynamicObject,
IDataRepository<TEntity>
where TEntity : class, new()
where TContext : DbContext, new()
{
protected TContext context;
protected DbSet<TEntity> DbSet;
}
As you can see, my abstract GenericRepository extends from DynamicObject to support dynamic repositories.
I also have a abstract UnitOfWork implementation which generated a repository for a given entity at runtime like this. Again, base classes and other details are irrelevant for the question, but I'm happy to provide them if you require.
public abstract class UnitOfWorkBase<TContext> : IUnitOfWork
where TContext : DbContext, new()
{
public abstract IDataRepository<T> Repository<T>()
where T : class, IIdentifiableEntity, new();
// Code
}
Following class implements abstract method of the above class.
public class MyUnitOfWorkBase : UnitOfWorkBase<MyDataContext>
{
public override IDataRepository<T> Repository<T>()
{
if (Repositories == null)
Repositories = new Hashtable();
var type = typeof(T).Name;
if (!Repositories.ContainsKey(type))
{
var repositoryType = typeof(GenericRepositoryImpl<,>);
var genericType = repositoryType.MakeGenericType(typeof(T), typeof(InTeleBillContext));
var repositoryInstance = Activator.CreateInstance(genericType);
Repositories.Add(type, repositoryInstance);
}
return (IDataRepository<T>)Repositories[type];
}
}
Now, whenever I want to create a dynamic repository for basic CRUD functions, I can do it like this.
var uow = new MyUnitOfWorkBase();
var settingsRepo = uow.Repository<Settings>();
var settingsList = settingsRepo.Get().ToList();
Now, What I want to do is something like this.
dynamic settingsRepo = uow.Repository<Settings>();
var result = settingsRepo.FindSettingsByCustomerNumber(774278L);
Here, FindSettingsByCustomerNumber() is a dynamic method. I resolve this method using this code.
public class GenericRepositoryImpl<TEntity, TContext> :
GenericRepository<TEntity, TContext>
where TEntity : class, IIdentifiableEntity, new()
where TContext : DbContext, new()
{
public override bool TryInvokeMember(InvokeMemberBinder binder,
object[] args, out object result)
{
// Crude parsing for simplicity
if (binder.Name.StartsWith("Find"))
{
int byIndex = binder.Name.IndexOf("By");
if (byIndex >= 0)
{
string collectionName = binder.Name.Substring(4, byIndex - 4);
string[] attributes = binder.Name.Substring(byIndex + 2)
.Split(new[] { "And" }, StringSplitOptions.None);
var items = DbSet.ToList();
Func<TEntity, bool> predicate = entity => entity.GetType().GetProperty(attributes[0]).GetValue(entity).Equals(args[0]);
result = items.Where(predicate).ToList();
return true;
}
}
return base.TryInvokeMember(binder, args, out result);
}
}
This is the problem I am having.
using this line var items = DbSet.ToList(); works well, but if I were to query a large table with 1000's of data, then performance issues occur.
If I directly try to use the IQueryble interface and call it like this
Func predicate = entity => entity.GetType().GetProperty(attributes[0]).GetValue(entity).Equals(args[0]);
result = DbSet.Where(predicate).ToList();
It gives me an error saying there is no method GetProperty() in LINQ to Entities.
Is it possible to make it work using LINQ to Entities?
You need to know that LINQ-to-Entities needs to convert your expression (given by the predicate) into a SQL query. entity is replaced by the database column. Additionally LINQ2Entities supports various expressions (e.g. EqualExpression, etc.). However it cannot support the whole .NET Framework. Especially: what should GetType() on a database column return?
Therefore you need to use the Expresson API to generate the predicate and use only expressions supported by LINQ2Entities. For example: Use a MemberAccess expression for accessing a property (LINQ2Entities is able to map that to an SQL query).
Hint: we are doing predicate generation for Entity Framework and had to overcome some additional problems which we could solve using the library LinqKit.
If you do not know about the .NET Expression API yet, you need to gather skills in that area before you can resume your dynamic repository idea.
BTW: I don't think that it is a very good idea to have this kind of automatic calls. They are not refactoring safe (i.e. what if you rename the DB column? All your method calls run into problems, and it is not detectable by the compiler).
I would use it only to generate predicates for Where() clauses from Filter-like DTO types.
Unusual pattern - dynamic methods on a repository patterns.But that is another topic.
Dynamic invocation of the repository you have.
So now you need to understand Linq to Entities a little more.
Linq to Entities language reference what you can do with linq to Entities.
Given the expression tree has to be converted in to DB instructions,
it isnt surprising there are restrictions.
In case you are interested The EF provider specs and links to samples
So given you want to Dynamic EF, you have a few options.
I concentrate on dynamic wheres, but you can apply to other EF methods.
Check out
Dynamic Linq on codeplex
which allows things like
public virtual IQueryable<TPoco> DynamicWhere(string predicate, params object[] values) {
return Context.Set<TPoco>().Where(predicate, values);
}
This Where is an IQueryable extension that accepts strings...
Samples of using this string based predicate parser
LinqKit or even PM> Install-Package LinqKit
Linqkit takes dynamic EF to the next level,
Offers amazing features like
public IQueryable<TPoco> AsExpandable() {
return Context.Set<TPoco>().AsExpandable();
}
which allows you build AND and ORs progressively.
Expression trees
Expression Building API is the most powerful tool to support you here .
Learning the API is hard. using the tool harder.
eg Dealing with concatenation very hard. BUT if you can understand the API and how expressions work.
It is possible.
Here is a SIMPLE example. (imagine something complex)
public static Expression<Func<TPoco, bool>> GetContainsPredicate<TPoco>(string propertyName,
string containsValue)
{
// (tpoco t) => t.propertyName.Contains(value ) is built
var parameterExp = Expression.Parameter(typeof(TPoco), #"t");
var propertyExp = Expression.Property(parameterExp, propertyName);
MethodInfo method = typeof(string).GetMethod(#"Contains", new[] { typeof(string) });
var someValue = Expression.Constant(containsValue, typeof(string));
var containsMethodExp = Expression.Call(propertyExp, method, someValue);
return Expression.Lambda<Func<TPoco, bool>>(containsMethodExp, parameterExp);
}
I've implemented the specification pattern with Linq as outlined here https://www.packtpub.com/article/nhibernate-3-using-linq-specifications-data-access-layer
I now want to add the ability to eager load and am unsure about the best way to go about it.
The generic repository class in the linked example:
public IEnumerable<T> FindAll(Specification<T> specification)
{
var query = GetQuery(specification);
return Transact(() => query.ToList());
}
public T FindOne(Specification<T> specification)
{
var query = GetQuery(specification);
return Transact(() => query.SingleOrDefault());
}
private IQueryable<T> GetQuery(
Specification<T> specification)
{
return session.Query<T>()
.Where(specification.IsSatisfiedBy());
}
And the specification implementation:
public class MoviesDirectedBy : Specification<Movie>
{
private readonly string _director;
public MoviesDirectedBy(string director)
{
_director = director;
}
public override
Expression<Func<Movie, bool>> IsSatisfiedBy()
{
return m => m.Director == _director;
}
}
This is working well, I now want to add the ability to be able to eager load. I understand NHibernate eager loading can be done by using Fetch on the query.
What I am looking for is whether to encapsulate the eager loading logic within the specification or to pass it into the repository, and also the Linq/expression tree syntax required to achieve this (i.e. an example of how it would be done).
A possible solution would be to extend the Specification class to add:
public virtual IEnumerable<Expression<Func<T, object>>> FetchRelated
{
get
{
return Enumerable.Empty<Expression<Func<T, object>>>();
}
}
And change GetQuery to something like:
return specification.FetchRelated.Aggregate(
session.Query<T>().Where(specification.IsSatisfiedBy()),
(current, related) => current.Fetch(related));
Now all you have to do is override FetchRelated when needed
public override IEnumerable<Expression<Func<Movie, object>>> FetchRelated
{
get
{
return new Expression<Func<Movie, object>>[]
{
m => m.RelatedEntity1,
m => m.RelatedEntity2
};
}
}
An important limitation of this implementation I just wrote is that you can only fetch entities that are directly related to the root entity.
An improvement would be to support arbitrary levels (using ThenFetch), which would require some changes in the way we work with generics (I used object to allow combining different entity types easily)
You wouldn't want to put the Fetch() call into the specification, because it's not needed. Specification is just for limiting the data that can then be shared across many different parts of your code, but those other parts could have drastically different needs in what data they want to present to the user, which is why at those points you would add your Fetch statements.
I am using Entity Framework 4.0 and trying to use the "Contains" function of one the object sets in my context object. to do so i coded a Comparer class:
public class RatingInfoComparer : IEqualityComparer<RatingInfo>
{
public bool Equals(RatingInfo x, RatingInfo y)
{
var a = new {x.PlugInID,x.RatingInfoUserIP};
var b = new {y.PlugInID,y.RatingInfoUserIP};
if(a.PlugInID == b.PlugInID && a.RatingInfoUserIP.Equals(b.RatingInfoUserIP))
return true;
else
return false;
}
public int GetHashCode(RatingInfo obj)
{
var a = new { obj.PlugInID, obj.RatingInfoUserIP };
if (Object.ReferenceEquals(obj, null))
return 0;
return a.GetHashCode();
}
}
when i try to use the comparer with this code:
public void SaveRatingInfo2(int plugInId, string userInfo)
{
RatingInfo ri = new RatingInfo()
{
PlugInID = plugInId,
RatingInfoUser = userInfo,
RatingInfoUserIP = "192.168.1.100"
};
//This is where i get the execption
if (!context.RatingInfoes.Contains<RatingInfo>(ri, new RatingInfoComparer()))
{
//my Entity Framework context object
context.RatingInfoes.AddObject(ri);
context.SaveChanges();
}
}
i get an execption:
"LINQ to Entities does not recognize the method 'Boolean Contains[RatingInfo](System.Linq.IQueryable1[OlafCMSLibrary.Models.RatingInfo], OlafCMSLibrary.Models.RatingInfo,
System.Collections.Generic.IEqualityComparer1[OlafCMSLibrary.Models.RatingInfo])' method, and his method cannot be translated into a store expression."
Since i am not proficient with linQ and Entity Framework i might be making a mistake with my use of the "var" either in the "GetHashCode" function or in general.
If my mistake is clear to you do tell me :) it does not stop my project! but it is essential for me to understand why a simple comparer doesnt work.
Thanks
Aaron
LINQ to Entities works by converting an expression tree into queries against an object model through the IQueryable interface. This means than you can only put things into the expression tree which LINQ to Entities understands.
It doesn't understand the Contains method you are using, so it throws the exception you see. Here is a list of methods which it understands.
Under the Set Methods section header, it lists Contains using an item as supported, but it lists Contains with an IEqualityComparer as not supported. This is presumably because it would have to be able to work out how to convert your IEqualityComparer into a query against the object model, which would be difficult. You might be able to do what you want using multiple Where clauses, see which ones are supported further up the document.
I have an XML file like this:
<SiteConfig>
<Sites>
<Site Identifier="a" />
<Site Identifier="b" />
<Site Identifier="c" />
</Sites>
</SiteConfig>
The file is user-editable, so I want to provide reasonable error message in case I can't properly parse it. I could probably write a .xsd for it, but that seems kind of overkill for a simple file.
So anyway, when querying for the list of <Site> nodes, there's a couple of ways I could do it:
var doc = XDocument.Load(...);
var siteNodes = from siteNode in
doc.Element("SiteConfig").Element("Sites").Elements("Site")
select siteNode;
But the problem with this is that if the user has not included the <SiteUrls> node (say) it'll just throw a NullReferenceException which doesn't really say much to the user about what actually went wrong.
Another possibility is just to use Elements() everywhere instead of Element(), but that doesn't always work out when coupled with calls to Attribute(), for example, in the following situation:
var siteNodes = from siteNode in
doc.Elements("SiteConfig")
.Elements("Sites")
.Elements("Site")
where siteNode.Attribute("Identifier").Value == "a"
select siteNode;
(That is, there's no equivalent to Attributes("xxx").Value)
Is there something built-in to the framework to handle this situation a little better? What I would prefer is a version of Element() (and of Attribute() while we're at it) that throws a descriptive exception (e.g. "Looking for element <xyz> under <abc> but no such element was found") instead of returning null.
I could write my own version of Element() and Attribute() but it just seems to me like this is such a common scenario that I must be missing something...
You could implement your desired functionality as an extension method:
public static class XElementExtension
{
public static XElement ElementOrThrow(this XElement container, XName name)
{
XElement result = container.Element(name);
if (result == null)
{
throw new InvalidDataException(string.Format(
"{0} does not contain an element {1}",
container.Name,
name));
}
return result;
}
}
You would need something similar for XDocument. Then use it like this:
var siteNodes = from siteNode in
doc.ElementOrThrow("SiteConfig")
.ElementOrThrow("SiteUrls")
.Elements("Sites")
select siteNode;
Then you will get an exception like this:
SiteConfig does not contain an element SiteUrls
You could use XPathSelectElements
using System;
using System.Linq;
using System.Xml.Linq;
using System.Xml.XPath;
class Program
{
static void Main()
{
var ids = from site in XDocument.Load("test.xml")
.XPathSelectElements("//SiteConfig/Sites/Site")
let id = site.Attribute("Identifier")
where id != null
select id;
foreach (var item in ids)
{
Console.WriteLine(item.Value);
}
}
}
Another thing that comes to mind is to define an XSD schema and validate your XML file against this schema. This will generate meaningful error messages and if the file is valid you can parse it without problems.