I'm looking for a bit of help with populating a Dictionary using a csv file within a WebService however Im unable to return the results.
Im tring to seperate the dictionary into two seperate columns which seemingly works but I cannot return the values as there are two and not one.
Here is the code:
{
StreamReader streamReader = new StreamReader("T:/4 Year WBL/Applications Development/Coursework 2/2b/Coursework2bwebservice/abrev.csv");
[WebMethod]
public string Dictionary()
{
string line;
Dictionary<string, string> dictionary = new Dictionary<string,string>();
while ((line = streamReader.ReadLine()) !=null)
{
string[] columns = line.Split(',');
dictionary.Add(columns[0], columns[1]);
return dictionary;
}
}
I am getting the error "cannot implicitly convert type System.Collections.Generic.Dictionary<string,string to string>"
Any ideas would be great and thank you for your time.
public string Dictionary()
is returning the wrong signature. You need to return an actual dictionary:
public Dictionary<string, string> Dictionary()
Also, this
while ((line = streamReader.ReadLine()) !=null)
seems a bit hinky. You're also returning your dictionary inside the loop. Let's try instead:
line = streamReader.Readline();
while (line !=null)
{
string[] columns = line.Split(',');
dictionary.Add(columns[0], columns[1]);
line = streamReader.Readline();
}
return dictionary;
All that said, returning an actual dictionary object in a web method probably doesn't make much sense. What you really want is an XML-serialized dictionary or list. See here: https://www.google.com/search?q=return+dictionary+in+web+method for more information.
Related
Simple.OData.Client has a typed and dynamic (and basic) syntax.
I like the typed, but I don't want to build out all my types. In the end I really only need two or so types in the results I get.
But my queries need more types to properly filter the results.
So I want to use the dynamic syntax. But I want to cast the results to classes I have.
I can easily do this manually, but I thought I would see if Simple.OData.Client supports this before I go writing up all that conversion code for each query.
Here is some dynamic syntax code that runs without errors:
client.For(x.Client).Top(10).Select(x.ClientId, x.Name).FindEntriesAsync();
Here is an example of what I had hoped would work (selecting into a new Client object)
client.For(x.Client).Top(10).Select(new Client(x.ClientId, x.Name)).FindEntriesAsync();
But that kind of projection is not supported (I get an "has some invalid arguments" error).
Is there a way to support projection into an existing class when using the dynamic syntax of Simple.OData.Client?
EDIT: The code below works. But it's performance is terrible. I decided to abandon it and write hand written mappers for each type I needed.
This is what I came up with:
dynamic results = oDataClient.For(x.Client).Select(x.ClientId, x.Name).FindEntriesAsync().Result;
var listOfClients = SimpleODataToList<Client>(results);
public List<T> SimpleODataToList<T>(dynamic sourceObjects) where T : new()
{
List<T> targetList = new List<T>();
foreach (var sourceObject in sourceObjects)
{
// This is a dictionary with keys (properties) and values. But no
// matter what sourceObject is passed in, the values will always be
// the values of the first entry in the sourceObjects list.
var sourceProperties = ((System.Collections.Generic.IDictionary<string, object>)sourceObject);
var targetProperties = typeof(Client).GetProperties().Where(prop => prop.CanWrite);
var targetObject = new T();
foreach (var targetProperty in targetProperties)
{
if (sourceProperties.ContainsKey(targetProperty.Name))
{
var sourceValue = GetProperty(sourceObject, targetProperty.Name);
targetProperty.SetValue(targetObject, sourceValue, null);
}
}
targetList.Add(targetObject);
}
return targetList;
}
public static object GetProperty(object o, string member)
{
if (o == null) throw new ArgumentNullException("o");
if (member == null) throw new ArgumentNullException("member");
Type scope = o.GetType();
IDynamicMetaObjectProvider provider = o as IDynamicMetaObjectProvider;
if (provider != null)
{
ParameterExpression param = Expression.Parameter(typeof(object));
DynamicMetaObject mobj = provider.GetMetaObject(param);
GetMemberBinder binder = (GetMemberBinder)Microsoft.CSharp.RuntimeBinder.Binder.GetMember(0, member, scope, new CSharpArgumentInfo[] { CSharpArgumentInfo.Create(0, null) });
DynamicMetaObject ret = mobj.BindGetMember(binder);
BlockExpression final = Expression.Block(
Expression.Label(CallSiteBinder.UpdateLabel),
ret.Expression
);
LambdaExpression lambda = Expression.Lambda(final, param);
Delegate del = lambda.Compile();
return del.DynamicInvoke(o);
}
else
{
return o.GetType().GetProperty(member, BindingFlags.Public | BindingFlags.Instance).GetValue(o, null);
}
}
It was made much harder because normal casts and such for the dynamic objects returned would only give the first object in the list over and over. The GetProperty method works around this limitation.
I have a dictionary:
Dictionary<string, long> Reps = new Dictionary<string, long>();
and I want to update the values while iterating through all items, like this:
foreach (string key in Reps.keys)
{
Reps[key] = 0;
}
it is giving me an error saying:
"Collection was modified; enumeration operation may not execute"
can anyone tell me why it is giving me this error, because I have one more function that adds the value, and it is called when button is clicked:
public static void Increment(string RepId, int amount)
{
long _value = Convert.ToInt64(Reps[RepId]);
_value = _value + amount;
Reps[RepId] = _value;
}
and this function is working fine. so whats the problem when updating all the values? And whats the solution for this?
more simplified, do this:
foreach (string key in Reps.keys.ToList())
{
Reps[key] = 0;
}
and the reason for the error is you are trying to edit the actual object which is in use and if you make a copy of it and then use it like this:
var repscopy = Reps;
foreach (string key in repscopy.keys)
{
Reps[key] = 0;
}
it'll give the same error as it also pointing to the original object, and when the ToList() is added it created a new object of List
The problem is no updating the values, you just cannot change the collection that your foreach() is based on while the foreach is being iterated.
Try somehting like this
List<string> keylist = Reps.keys.ToList();
foreach(string r in keylist)
{
Reps[r] = 0;
}
this would work.
This happens because you are changing the element in the Dictionary<string, long> while looping over it with foreach. Try this.
foreach (string key in Reps.Keys.ToList())
{
Reps[key] = 0;
}
Now you are looping over a list created from the dictionarys key. As it is not the original collection thats modified, the error will go away.
Not really sure how to do this but i can cache the dictionary like this:
Cache.Insert("CacheName", Dictionary)
need some direction. the dictionary is two string values taken from a database. The user will input a string and i need to compare it against the values in the cached dictionary.
In general you need to access the object from the cache, cast it, and the use the ContainsKey property. Here is an example:
First add the dictionary to the Cache:
IDictionary<string, string> testDict = new Dictionary<string, string>();
testDict.Add("Test", "test");
Cache.Insert("dict", testDict);
Then, when you need to do so, access the cached object and use it ContainsKey property to determine whether it contains the searched key or not.
var dict = Cache["dict"] as IDictionary<string, string>;
if (dict != null)
{
string testValue = "test";
if(dict.ContainsKey(testValue))
{
/* some logic here */
}
}
You can access the value the following way:
if (dict != null)
{
string testValue = "test";
if(dict.ContainsKey(testValue))
{
/* some logic here */
string value = dict[testValue];
}
}
You can get the dictionary out of the cache by writing
var dict = (Dictionary<X, Y>) cache["CacheName"];
I know i can do this
var nv = HttpUtility.ParseQueryString(req.RawUrl);
But is there a way to convert this back to a url?
var newUrl = HttpUtility.Something("/page", nv);
Simply calling ToString() on the NameValueCollection will return the name value pairs in a name1=value1&name2=value2 querystring ready format. Note that NameValueCollection types don't actually support this and it's misleading to suggest this, but the behavior works here due to the internal type that's actually returned, as explained below.
Thanks to #mjwills for pointing out that the HttpUtility.ParseQueryString method actually returns an internal HttpValueCollection object rather than a regular NameValueCollection (despite the documentation specifying NameValueCollection). The HttpValueCollection automatically encodes the querystring when using ToString(), so there's no need to write a routine that loops through the collection and uses the UrlEncode method. The desired result is already returned.
With the result in hand, you can then append it to the URL and redirect:
var nameValues = HttpUtility.ParseQueryString(Request.QueryString.ToString());
string url = Request.Url.AbsolutePath + "?" + nameValues.ToString();
Response.Redirect(url);
Currently the only way to use a HttpValueCollection is by using the ParseQueryString method shown above (other than reflection, of course). It looks like this won't change since the Connect issue requesting this class be made public has been closed with a status of "won't fix."
As an aside, you can call the Add, Set, and Remove methods on nameValues to modify any of the querystring items before appending it. If you're interested in that see my response to another question.
string q = String.Join("&",
nvc.AllKeys.Select(a => a + "=" + HttpUtility.UrlEncode(nvc[a])));
Make an extension method that uses a couple of loops. I prefer this solution because it's readable (no linq), doesn't require System.Web.HttpUtility, and it supports duplicate keys.
public static string ToQueryString(this NameValueCollection nvc)
{
if (nvc == null) return string.Empty;
StringBuilder sb = new StringBuilder();
foreach (string key in nvc.Keys)
{
if (string.IsNullOrWhiteSpace(key)) continue;
string[] values = nvc.GetValues(key);
if (values == null) continue;
foreach (string value in values)
{
sb.Append(sb.Length == 0 ? "?" : "&");
sb.AppendFormat("{0}={1}", Uri.EscapeDataString(key), Uri.EscapeDataString(value));
}
}
return sb.ToString();
}
Example
var queryParams = new NameValueCollection()
{
{ "order_id", "0000" },
{ "item_id", "1111" },
{ "item_id", "2222" },
{ null, "skip entry with null key" },
{ "needs escaping", "special chars ? = &" },
{ "skip entry with null value", null }
};
Console.WriteLine(queryParams.ToQueryString());
Output
?order_id=0000&item_id=1111&item_id=2222&needs%20escaping=special%20chars%20%3F%20%3D%20%26
This should work without too much code:
NameValueCollection nameValues = HttpUtility.ParseQueryString(String.Empty);
nameValues.Add(Request.QueryString);
// modify nameValues if desired
var newUrl = "/page?" + nameValues;
The idea is to use HttpUtility.ParseQueryString to generate an empty collection of type HttpValueCollection. This class is a subclass of NameValueCollection that is marked as internal so that your code cannot easily create an instance of it.
The nice thing about HttpValueCollection is that the ToString method takes care of the encoding for you. By leveraging the NameValueCollection.Add(NameValueCollection) method, you can add the existing query string parameters to your newly created object without having to first convert the Request.QueryString collection into a url-encoded string, then parsing it back into a collection.
This technique can be exposed as an extension method as well:
public static string ToQueryString(this NameValueCollection nameValueCollection)
{
NameValueCollection httpValueCollection = HttpUtility.ParseQueryString(String.Empty);
httpValueCollection.Add(nameValueCollection);
return httpValueCollection.ToString();
}
Actually, you should encode the key too, not just value.
string q = String.Join("&",
nvc.AllKeys.Select(a => $"{HttpUtility.UrlEncode(a)}={HttpUtility.UrlEncode(nvc[a])}"));
Because a NameValueCollection can have multiple values for the same key, if you are concerned with the format of the querystring (since it will be returned as comma-separated values rather than "array notation") you may consider the following.
Example
var nvc = new NameValueCollection();
nvc.Add("key1", "val1");
nvc.Add("key2", "val2");
nvc.Add("empty", null);
nvc.Add("key2", "val2b");
Turn into: key1=val1&key2[]=val2&empty&key2[]=val2b rather than key1=val1&key2=val2,val2b&empty.
Code
string qs = string.Join("&",
// "loop" the keys
nvc.AllKeys.SelectMany(k => {
// "loop" the values
var values = nvc.GetValues(k);
if(values == null) return new[]{ k };
return nvc.GetValues(k).Select( (v,i) =>
// 'gracefully' handle formatting
// when there's 1 or more values
string.Format(
values.Length > 1
// pick your array format: k[i]=v or k[]=v, etc
? "{0}[]={1}"
: "{0}={1}"
, k, HttpUtility.UrlEncode(v), i)
);
})
);
or if you don't like Linq so much...
string qs = nvc.ToQueryString(); // using...
public static class UrlExtensions {
public static string ToQueryString(this NameValueCollection nvc) {
return string.Join("&", nvc.GetUrlList());
}
public static IEnumerable<string> GetUrlList(this NameValueCollection nvc) {
foreach(var k in nvc.AllKeys) {
var values = nvc.GetValues(k);
if(values == null) { yield return k; continue; }
for(int i = 0; i < values.Length; i++) {
yield return
// 'gracefully' handle formatting
// when there's 1 or more values
string.Format(
values.Length > 1
// pick your array format: k[i]=v or k[]=v, etc
? "{0}[]={1}"
: "{0}={1}"
, k, HttpUtility.UrlEncode(values[i]), i);
}
}
}
}
As has been pointed out in comments already, with the exception of this answer most of the other answers address the scenario (Request.QueryString is an HttpValueCollection, "not" a NameValueCollection) rather than the literal question.
Update: addressed null value issue from comment.
The short answer is to use .ToString() on the NameValueCollection and combine it with the original url.
However, I'd like to point out a few things:
You cant use HttpUtility.ParseQueryString on Request.RawUrl. The ParseQueryString() method is looking for a value like this: ?var=value&var2=value2.
If you want to get a NameValueCollection of the QueryString parameters just use Request.QueryString().
var nv = Request.QueryString;
To rebuild the URL just use nv.ToString().
string url = String.Format("{0}?{1}", Request.Path, nv.ToString());
If you are trying to parse a url string instead of using the Request object use Uri and the HttpUtility.ParseQueryString method.
Uri uri = new Uri("<THE URL>");
var nv = HttpUtility.ParseQueryString(uri.Query);
string url = String.Format("{0}?{1}", uri.AbsolutePath, nv.ToString());
I always use UriBuilder to convert an url with a querystring back to a valid and properly encoded url.
var url = "http://my-link.com?foo=bar";
var uriBuilder = new UriBuilder(url);
var query = HttpUtility.ParseQueryString(uriBuilder.Query);
query.Add("yep", "foo&bar");
uriBuilder.Query = query.ToString();
var result = uriBuilder.ToString();
// http://my-link.com:80/?foo=bar&yep=foo%26bar
In AspNet Core 2.0 you can use QueryHelpers AddQueryString method.
As #Atchitutchuk suggested, you can use QueryHelpers.AddQueryString in ASP.NET Core:
public string FormatParameters(NameValueCollection parameters)
{
var queryString = "";
foreach (var key in parameters.AllKeys)
{
foreach (var value in parameters.GetValues(key))
{
queryString = QueryHelpers.AddQueryString(queryString, key, value);
}
};
return queryString.TrimStart('?');
}
This did the trick for me:
public ActionResult SetLanguage(string language = "fr_FR")
{
Request.UrlReferrer.TryReadQueryAs(out RouteValueDictionary parameters);
parameters["language"] = language;
return RedirectToAction("Index", parameters);
}
You can use.
var ur = new Uri("/page",UriKind.Relative);
if this nv is of type string you can append to the uri first parameter.
Like
var ur2 = new Uri("/page?"+nv.ToString(),UriKind.Relative);
My Question is how do I handle a null set returned from a linq query if I am loading it into a custom class.
example
queryResults = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT).ToList<specialItems>();
...
public class specialItems
{
public string Id { get; set; }
public string Section { get; set; }
public string Program { get; set; }
public string Event { get; set; }
public courseItems(string id, string section, string program, string event)
{
this.Id = id;
this.Section = section;
this.Program = program;
this.Event = event;
}
}
Currently this query works great until the result set is empty, then I get:
"Object reference not set to an instance of an object."
I need the query to return an empty List if the result set is empty.
UPDATE - Asided from the invalid redeclaration of a variable (fixed) I did find that the issue was higher up in the initial construction of the linq query. This became apparent when I received several good suggestions and removed the error. Once I fixed the original query things worked swimmingly.
Use the null coalescing operator (??).
List<specialItems> queryResults = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT).ToList<specialItems>() ?? new List<specialItems>();
EDIT: Yeah, looking at what you have there a little closer, it's the ToList that's blowing up when this happens. You might have to split it up a bit.
var temp = queryResults.Select(p => new specialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT);
List<specialItems> results = temp == null ? new List<specialItems>() : temp.ToList<SpecialItems>();
Have to do it this way, because there's no good spot to put the null coalescing operator in this case.
Robaticus is mostly right, use the null coalescing operator (??). Howerver, since you didn't include the stack trace, I assume your code is throwing because queryResults is initially null. By the time you get to the ?? operator, you've already thrown the exception, because you tried to dereference queryResults.
Also, the code you have doesn't make a ton of sense, because queryResults is already defined within that scope by the time you get to that line. You can't redefine a variable that has already been declared locally in that scope.
List<SpecialItems> queryResults = GetSomeResults();
queryResults = (queryResults ?? new List<SpecialItems>())
.Select(p => new SpecialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT))
.ToList<SpecialItems>();
If you can get the function or line that spits out the original version of queryResults to return an empty list instead of null, then try to do that, or coalesce the results on that line. That's probably better than having all that code on the query line :)
List<SpecialItems> queryResults = GetSomeResults() ?? new List<SpecialItems>();
queryResults = queryResults
.Select(p => new SpecialItems(p.ID, p.SECTION, p.PROGRAM, p.EVENT))
.ToList<SpecialItems>();
Linq returns an empty list if there are no results, never null. Therefore, the problem is certainly not that queryResults.Select() returns null.
What is probably going on is that we're looking at a lazily evaluated linq-to-objects 'query'. ToList() triggers the evaluation of it, and probably the nullreference exception occurs in a lambda expression higher up the chain.
Neither Enumerable.Select, nor Queryable.Select, nor Enumerable.ToList return null.
The query is not realized until ToList enumerates it. During that enumeration, a null reference exception is occuring due to code you have not posted in the question.
Consider this code with and without the commented line:
List<int> source = Enumerable.Range(1, 10).ToList();
IEnumerable<int> query = null;
try
{
query = source.Where(i => 1 / i > 0);
}
catch(Exception ex)
{
Console.WriteLine("Exception was caught {0}", ex.Message);
}
// source.Add(0);
List<int> result = query.ToList();
Consider this code with and without the commented line:
DataContext myDC = new DataContext();
string name = null;
IQueryable<Person> query = myDC.Persons.Where(p => p.Name.StartsWith(name));
// name = "Zz";
List<Person> result = query.ToList();