I'd like to use an action filter to translate an Odata uri to a Linq expression. I'm doing this because i'm using the resulting expression to query nonSQL line of business systems. In the WCF web api this was trivial because the translated query was appended as a property of the the request object, as such:
var query = (EnumerableQuery)request.Properties["queryToCompose"];
That seems to have disappeared. Are there any public api's i can use to accomplish this?
I've been trying something similiar.. While not perfect, you can grab the OData expressions directly from the query string and build the LINQ expression manually:
var queryParams = HttpUtility.ParseQueryString( ControllerContext.Request.RequestUri.Query );
var top = queryParams.Get( "$top" );
var skip = queryParams.Get( "$skip" );
var orderby = queryParams.Get( "$orderby" );
And the apply that directly to your IQueryable or whatever you're using for the filtering. Not nearly as useful, but its a start.
So as it turns out the query has changed keys in the request property collection. It also seems that the internal filter that parses the query runs after the custom filters and thus doesn't add the query value. To get the translated query, call the following inside the controller action.
(EnumerableQuery<T>)this.Request.Properties["MS_QueryKey"];
Check out Linq2Rest. It solves this problem.
Related
I'm trying to perform a LIKE clause in an entity query. The examples I've seen use dynamic linq to do this kind of thing, but my code...
var query = context.StudySet
.Where("it.PatientName LIKE #patientName", new ObjectParameter("patientName", patientName);
...gives me a System.Linq.Dynamic.ParseException with
Additional information: Expression of type 'Boolean' expected
context is a DbContext from EF 6 code-first, patientName is a string
Please tell me what's wrong with my code?
if you want use DynamicLINQ you need change your code like this
var query = context.StudySet.Where("it.PatientName.Contains(#0)", patientName);
because DynamicLinq can't parse LIKE operator
I've realised my mistake.
I had assumed the method to pass the query was part of Dynamic Linq but actually it's just a variant of the standard Where method on ObjectQuery. If I get the ObjectContext from my (code first) DbContext it's all good.
ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;
ObjectSet<Study> studySet = objectContext.CreateObjectSet<Study>();
var query = studySet.
Where("it.PatientName LIKE #patientName", new ObjectParameter("patientName", patientName));
I don't know of a way to use like with a LINQ query, but you could use a raw SQL query:
var query = context.StudySet.SqlQuery(
"select * from StudySet where PatientName LIKE #patientName",
new SqlParameter("#patientName", patientName));
I am new to LINQ queries and to EF too, I usually work with MySQL and I can't guess how to write really simples queries.
I'd like to select all results from a table. So, I used like this:
ZXContainer db = new ZXContainer();
ViewBag.ZXproperties = db.ZXproperties.All();
But I see that I have to write something inside All(---).
Could someone guide me in how could I do that? And if someone has any good link for references too, I thank so much.
All() is an boolean evaluation performed on all of the elements in a collection (though immediately returns false when it reaches an element where the evaluation is false), for example, you want to make sure that all of said ZXproperties have a certain field set as true:
bool isTrue = db.ZXproperties.All(z => z.SomeFieldName == true);
Which will either make isTrue true or false. LINQ is typically lazy-loading, so if you're calling db.ZXproperties directly, you have access to all of the objects as is, but it isn't quite what you're looking for. You can either load all of the objects at the variable assignment with an .ToList():
ViewBag.ZXproperties = db.ZXproperties.ToList();
or you can use the below expression:
ViewBag.ZXproperties = from s in db.ZXproperties
select s;
Which is really no different than saying:
ViewBag.ZXproperties = db.ZXproperties;
The advantage of .ToList() is that if you are wanting to do multiple calls on this ViewBag.ZXproperties, it will only require the initial database call when it is assigning the variable. Alternatively, if you do any form of queryable action on the data, such as .Where(), you'll have another query performed, which is less than ideal if you already have the data to work with.
To select everything, just skip the .All(...), as ZXproperties allready is a collection.
ZXContainer db = new ZXContainer();
ViewBag.ZXproperties = db.ZXproperties;
You might want (or sometimes even need) to call .ToList() on this collection before use...
You don't use All. Just type
ViewBag.ZXproperties = db.ZXproperties;
or
ViewBag.ZXproperties = db.ZXproperties.ToList();
The All method is used to determine if all items of collection match some condition.
If you just want all of the items, you can just use it directly:
ViewBag.ZXproperties = db.ZXproperties;
If you want this evaluated immediately, you can convert it to a list:
ViewBag.ZXproperties = db.ZXproperties.ToList();
This will force it to be pulled across the wire immediately.
You can use this:
var result = db.ZXproperties.ToList();
For more information on linq see 101 linq sample.
All is some checking on all items and argument in it, called lambda expression.
I think we are basically looking for a extension method that could take in an IQueryable and return an IQueryable based on an entire query statement and not just the where statement.
Example of what we would like for a Search Method:
IRepository<Person> repository = new Repository<Person>();
var results = repository.GetQuery().Include("Names").Search([dynamic linq here]);
We currently have where we build a dynamic linq statement inside the where method
IRepository<Person> repository = new Repository<Person>();
var results = repository.GetQuery().Include("Names").Where([dynamic linq here]);
The problem with that approach is that we want to do include SelectMany and Select on the actual dynamic linq query. You cannot use the SelectMany inside a Where method unless you are actually going into sub properties of sub properties. We would like to do something like the following dynamic linq statement.
SelectMany("Names").Where("LastName.Contains(#0)", "Smith").Select("Person")
We solved this issue without having to use a extension method. We were able to use a similar query that works inside a Where method.
So instead of...
SelectMany("Names").Where("LastName.Contains(#0)", "Smith").Select("Person")
We were able to get the same result with the following query that can be inside a Where method.
Where.("Names.Select(LastName).Contains(#0)", "Smith)
Then when just had to add a Contains Aggregate to the Dynamic Linq library.
http://blog.walteralmeida.com/2010/05/advanced-linq-dynamic-linq-library-add-support-for-contains-extension-.html
The SelectMany had sent us off on a wild goose chase!
Checkout this nuget package: NinjaNye.SearchExensions
It enables you to do something like the following:
var repository = new Repository<Person>();
var results = repository.GetQuery().Search(p => p.LastName, "Smith");
Connected to sql this will produce something smilar to the following:
SELECT [Extent1].[Id] AS [Id],
... [other properties],
[Extent1].[LastName] AS [LastName]
FROM [dbo].[Person] AS [Extent1]
WHERE ([Extent1].[LastName] LIKE N'%Smith%')
The query is built using expression trees so the result is clean.
Check out the source code here:
https://github.com/ninjanye/SearchExtensions/
Is there a way to use a LINQ expression to request a Count query from the Netflix oData service in Silverlight 4?
The Netflix documentation shows that you can return counts by appending $count to a request for a collection, but a URL like this:
http://netflix.cloudapp.net/Catalog/Genres/$count
Is not generated from an expression like this:
var count = (from g in catalog.Genres select g).Count();
The above code returns an error saying that the Count method is not supported. Is there a way to do this in LINQ, or do I just need to make WebClient request to get the value?
Count and LongCount are not supported in Silverligth because they require a synchornous execution of the query. Since Silverlight requires all network operations to by asynchronous this is not possible.
You can either issue the HTTP query in question programatically not using DataServiceContext (or related classes), since the $count returns a text representation of the number, parsing the response is not that hard.
Or you can use a bit of a trick. You can use IncludeTotalCount() to add $inlinecount=allpages query option to the query which will include the count in the response. Then to not download all the entities from server, you can use Take(0) which will add $top=0 and thus return empty result set. But the inline count will still contain the right number.
You can access the inline count on the QueryOperationResponse.TotalCount property.
Something like this:
NetflixCatalog ctx = new NetflixCatalog(new Uri("http://netflix.cloudapp.net/Catalog"));
var q = (DataServiceQuery<Genre>)ctx.Genres.IncludeTotalCount().Take(0);
q.BeginExecute((ar) =>
{
QueryOperationResponse<Genre> r = (QueryOperationResponse<Genre>)q.EndExecute(ar);
r.TotalCount.ToString(); // Use the count in whatever way you need
}, null);
It works in LinqPad 4 using C# 4.0
var count = (from g in Genres select g).Count();
count.Dump();
Result: 518
In LinqPad 2 using C# 3.0 the error appears.
Suppose I have a table Person(PersonID, Name, ....). Then I use EF to create a Entity model and then create DomainService based on Ria Service. At client side(sliverlight), I try to create a dynamic linq for filter function. What I did is:
q = EntityQuery<MyData.Person>
q = q.Where(p=> p.Name.Contains(NameVar));
That is fine. Then I have another two tables for phone:
Phone(PhoneID, PhoneNumber, ...)
PersonPhone(PersonID, PhoneID, ...)
Then I want to add filter to match PhoneNumber. How to write the linq query q like?
q = q.Where(p => p.PersonPhone.
Where(ph=>ph.PhoneNumber.Contains(PhoneVar)&& ph.PersonID == p.PersonID).Count()>0);
I can pass the compiliation, but when run the app, I got error:
Query operator 'Count' is not supported
How to resolve this problem?
This sounds like a good scenario for writing a custom query method on the server and invoking that method instead of the default query for Person. RIA Services only supports a subset of LINQ operations on the client, but you can use all LINQ operators on the server.
You need to use the QueryBuilder
Here's a sample
var qb = new QueryBuilder<Person>().Where(p => p.PersonPhone.Where(ph=>ph.PhoneNumber.Contains(PhoneVar)&& ph.PersonID == p.PersonID).Count()>0);
Then you can take qb and apply it to whatever query you like.
query = qb.ApplyTo(query);
By using Func<QueryBuilder<Person>> you can pass around your dynamic filter into common controls and etc. And when you invoke the function you'll get the current values from that ViewModel.