I need to translate the following Code to an Expression and I will explain why:
results = results.Where(answer => answer.Question.Wording.Contains(term));
results is IQueryable<ISurveyAnswer>
Question is ISurveyQuestion
Wording is String
The problem is, Question is not always the name of the LINQ to SQL property.
This will give me the PropertyInfo for the actual ISurveyQuestion property
private static PropertyInfo FindNaturalProperty<TMemberType>(Type search)
{
IDictionary<string,PropertyInfo> properties = new Dictionary<string,PropertyInfo>();
search.GetProperties().Each(prop =>
{
if (null != prop.PropertyType.GetInterface(typeof(TMemberType).Name))
properties.Add(prop.Name, prop);
});
if (properties.Count < 1) throw new ArgumentException(String.Format("{0} has no properties of type {1}", search.Name, typeof(TMemberType).Name));
if (properties.Count == 1) return properties.Values.First();
search.GetInterfaces().Each(inter =>
{
inter.GetProperties().Each(prop =>
{
if (null != prop.PropertyType.GetInterface(typeof(TMemberType).Name))
properties.Remove(prop.Name);
});
});
if (properties.Count < 1) throw new ArgumentException(String.Format("{0} has no properties of type {1} that are not members of an interface", search.Name, typeof(TMemberType).Name));
if (properties.Count > 1) throw new AmbiguousMatchException(String.Format("{0} has more than one property that are of type {1} and are not members of an interface", search.Name, typeof(TMemberType).Name));
return properties.Values.First();
}
Once I have the PropertyInfo how do I translate that to an Expression Tree?
EDIT:
What I basically need is:
results = results.Where(answer => answer.GetQuestionProperty().GetValue(answer).Wording.Contains(term));
But that doesn't work so I need to build the Expression Tree myself, for linq-to-sql.
Reading the question I think what you're after is Dynamic Linq - which is a helper library to let you build Linq queries dynamically (!) using strings as opposed to at design time. That means that if you can get your property name you should be able create your query on the fly.
ScottGu has an article here
What your trying to do is create a dynamic query and you want the action tables / properties your query against to be dynamic as well. I am not sure if this is easily possible based on how you want to use it.
Check out ScottGu's blog post:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
and
Check out Rick Strahl's blog post:
http://www.west-wind.com/Weblog/posts/143814.aspx
http://www.linqpad.net/
linqpad will convert it for you.
Related
I'm using EF5.0 in an ASP.NET MVC app. My Entity Model is named 'DataModel'. Included in the model is a table-valued function that exists in my MSSQL database, named MatchingEntries. It returns a table of integer ids.
I've looked at the DataModel.Context.cs file, that gets generated via the .tt (T4) template file. It has the following code in it:
[EdmFunction("DataEntities", "MatchingEntries")]
public virtual IQueryable<Nullable<int>> MatchingEntries(string term)
{
var termParameter = term != null ?
new ObjectParameter("Term", term) :
new ObjectParameter("Term", typeof(string));
return ((IObjectContextAdapter)this).ObjectContext.CreateQuery<Nullable<int>>("[DataEntities].[MatchingEntries](#Term)", termParameter);
}
The error I am getting results from using this method twice within the one query, such as:
IQueryable<int> one = db.MatchingEntries("\"one*\"");
IQueryable<int> two = db.MatchingEntries("\"two*\"");
List<int> both = one.Intersect(two).ToList();
The error is:
A parameter named 'Term' already exists in the parameter collection. Parameter names must be unique in the parameter collection.
Parameter name: parameter
Is this a known limitation of the classes generated from an EDMX for table-valued functions? With LINQ2SQL I am able to execute this a a single query to the database (that does a JOIN between the 2 outputs from MatchingEntries) and it replaces the parameter name #Term with #p0 and #p1 for the two different instances of the call. I'd like to make Entity Framework do the same.
So, my question is, how can I get EF to work in the same manner and avoid the 'Duplicate parameter' error?
My fallback is to evaluate each call to db.MatchingEntries separately, by putting ToList() after them. My other idea has been to replace the ObjectParameter name in the T4 generated Context.cs class with something randomly generated each time. These feel like hacks that I should be able to avoid.
This answer is Linq to Entities specific. This doesn't have to be done in Linq to SQL (Linqpad).
Thanks to this question I got a pointer to a viable solution:
extend the autogenerated DBContext class (partial class)
add a method with two parameters in the partial class
at calling, pass an index as second parameter
Detailed Answer:
DataEntitys.my.cs:
[EdmFunction("DataEntities", "MatchingEntries")]
public virtual IQueryable<Nullable<int>> MatchingEntries(string term, int index)
{
string param_name = String.Format("k_{0}", index);
var termParameter = term != null ?
new ObjectParameter(param_name, term) :
new ObjectParameter(param_name, typeof(string));
return ((IObjectContextAdapter)this).
ObjectContext.CreateQuery<Nullable<int>>(
String.Format("[DataEntities].[MatchingEntries](#{0})", param_name),
termParameter);
}
Call the function:
foreach (string teil in such)
{
index++;
if (teil.Trim() != "")
res = res.Join(db.MatchingEntries("\"" + teil + "*\"", index), l => l.ID, s => s.KEY, (l, s) => l);
}
I have Ienumerable<string> collection that I want to concatenate into a single string with delimitor ;
for instance {"One","Two","Three"} -> "One;Two;Three;"
is it possible to do using the following function?
List<string> list = new List<string>(){"One","Two","Three"};
list.Aggregate<String>((x,y) => x + String.Format("{0};",y));
I have tried also this code:
list.Aggregate<String>((x,y) => String.Format("{0};{1}",x,y));
both samples didn't work.
EDIT: I see that it is not possible to do what I wanted using Linq-2-sql or Aggregate function in Linq-2-sql.
http://social.msdn.microsoft.com/forums/en-US/linqprojectgeneral/thread/dac496c0-5b37-43ba-a499-bb8eff178706/
EDIT2: the workaround I used is to go over the items returned by the original linq query...and copies them to a new list and do the join as suggested in the answers below on a linq object and not linq-2-sql object.
You can just use String.Join for this. If you're using .NET4 then you can use the overload that takes an IEnumerable<string> directly:
string joined = string.Join(";", list);
If you're using an older version of the framework then you'll need to use the overload that takes a string[] array instead, converting your collection to an array first if necessary:
string joined = string.Join(";", list.ToArray());
EDIT...
Of course, if you really want to use Aggregate for some reason then there's nothing stopping you. If so, it's usually recommended to build your string using a StringBuilder rather than multiple string allocations:
string joined = list.Aggregate(new StringBuilder(),
(sb, s) => sb.Append(s).Append(';'),
sb => (sb.Length > 0) ? sb.ToString(0, sb.Length - 1)
: "");
You can do it using below code
list.Aggregate((i, j) => i + ";" + j);
You'll need to provide an initializer, otherwise the first element will not have a ; added to it:
list.Aggregate<String>("", (x,y) => x + String.Format("{0};",y));
my query is :
var ReadAndUnreadMessages =
(from m in MDB.Messages
orderby m.Date descending
where m.ID_Receive == (Guid)USER.ProviderUserKey && m.Delete_Admin == false
select new AllMessages()
{
id = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).ID_Message,
parent = (Guid)(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).ID_Message_Parent,
sender = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).ID_Sender,
receiver = (Guid)USER.ProviderUserKey,
subject = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Subject.Subject1.ToString() == "Other" ?
(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Other_Subject
:
(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Subject.Subject1.ToString(),
body = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Body.Length > 26 ?
(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Body.Substring(0, 25) + "..."
:
(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Body,
date = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).Date.ToShortDateString(),
read =(LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).IsRead,
finished = (LoadMessageChildren(m.ID_Message)[LoadMessageChildren(m.ID_Message).Count - 1] as Message).IsFinished,
count = MessageClass.LoadAll(m.ID_Message).Count
}).ToList();
and exception is :
The argument 'value' was the wrong type. Expected 'Message'. Actual 'System.Object'.
what does meaning it?
LoadMessageChildren :
public static ArrayList LoadMessageChildren(Guid Parent)
{
ArrayList arr = new ArrayList();
Guid id = Parent;
while (id != Guid.Empty)
{
arr.Add(LoadMessage(id));
try
{
id = (Guid)MDB.Messages.Single(a => a.ID_Message_Parent == id).ID_Message;
}
catch
{
id = Guid.Empty;
}
}
return arr;
}
LoadMessage :
public static Message LoadMessage(Guid id)
{
var mess = from m in MDB.Messages
where m.ID_Message == id
select m;
return mess.Single();
}
The code is unreadable, and as a bad case of code repetition (and multiple executions of LoadMessageChildren).
For starters, consider the following:
from m in MDB.Messages
orderby m.Date descending
where m.ID_Receive == (Guid)USER.ProviderUserKey && m.Delete_Admin == false
let children = LoadMessageChildren(m.ID_Message)
let lastChildMessage = children.Last()
select new AllMessages()
{
id = lastChildMessage.ID_Message,
...
}
This may solve your problem, as it is might be caused by using the [] indexer.
Aside from that, it is not clear the posted code is causing the exception.
The only thing I see you using LoadChildMessages() for in the end is to get the child message count... Unless I am wrong I would think you could write it as a join. You doing a lot of queries with in queries that don't seem necessary and are probably causing multiple hits to the database. My question to that would be why isn't there a relationship in your dmbl/sql database so that LinqToSql knows to create a property as a List<Message> ChildMessages
But here is my take:
var query = from message in MDB.Messges
join childmessage in MDB.Messages.Where(child => child.ID_Message_Parent == message.ID_Message) into childMessages
from childMessage in childMessages.DefaultIfEmpty() // This creates a
// left outer join so you get parent messages that don't have any children
where message.ID_Receive == (Guid)USER.ProviderUserKey && message.Delete_Admin == false
select new AllMessages()
{
id = message.ID_Message,
parent = message.ID_Message_Parent,
sender = message.ID_Sender,
receiver = (Guid)USER.ProviderUserKey,
subject = message.Subject.Subject1.ToString() == "Other" ?
message.Other_Subject
:
message.Subject.Subject1.ToString(),
body = message.Body.Length > 26 ?
message.Body.Substring(0, 25) + "..."
:
message.Body,
date = message.Date.ToShortDateString(),
read =message.IsRead,
finished = message.IsFinished,
count = childMessage.Count() // This might have to be this
//count = childMessage == null ? 0 : childMessage.Count()
};
var ReadAndUnreadMessages = query.ToList();
But it's hard to say because I can't run the code... Please respond and let me know if this works.
Note: May I suggest using a class that links to your DataContext.Log property that writes the generated TSQL code to the debugger window. Here is an article on writing your own. It has really help me know when I am making unnecessary calls to the database.
The error is most likely caused by the use of the ArrayList.
The problem is that LINQ was designed to work with generic collections that implement the System.Collections.Generic.IEnumerable<T> interface. The ArrayList is a nongeneric collection that internally stores everything as an Object. So when you retrieve something from the ArrayList you need to cast it to a Message.
Looking at your error message it looks like somewhere a Message object is expected, but the instance in your ArrayList (an Object) is not casted to a Message object when that reference occurs. Also, the ArrayList does not implement the IEnumerable<T> interface which might get you into trouble in certain situations also.
How to fix it?
I suggest changing the implementation of your LoadMessageChildren to use a generic list (List<Message>):
public static List<Message> LoadMessageChildren(Guid Parent)
{
List<Message> arr = new List<Message>();
Guid id = Parent;
while (id != Guid.Empty)
{
arr.Add(LoadMessage(id));
try
{
id = (Guid)MDB.Messages.Single(a => a.ID_Message_Parent == id).ID_Message;
}
catch
{
id = Guid.Empty;
}
}
return arr;
}
You will have to make also change the code that interacts with the generic list in terms of retrieving/referencing items. But that is just syntax. Since equivalent methods for dealist with lists and items exist.
There are also advantages in terms of performance and compile-time validation for switching from ArrayList to List<T>. The ArrayList is basically an inheritance from version 1.0 of the .Net Framework when there was no support for generics and it just get kept in the framework probably for compatibility reasons.
There are greater benefits for using generics.
UPDATED ANSWER:
The "Method 'System.Collections.Generic.List'1[Message] LoadMessageChildren(System.Guid)' has no supported translation to SQL" exception that you are getting is caused by the fact that your LoadMessageChildren method is not mapping to a stored procedure or a user defined function in your database.
You cannot have any regular C# method call inside your LINQ to SQL queries. The LINQ to SQL object model interprets a method found inside your query as either a stored procedure or a user defined function. So the engine is basically looking for a method called LoadMessageChildren that maps to a stored procedure or a user defined function in your database. Because there are no mappings, it tells you that no supported translation to SQL was found. The LINQ to SQL object model link shows you how to use method attributes to map a method that executes a stored procedure.
You have a few choices now:
create stored procedures of your regular C# method calls
rewrite your LINQ query to use joins to select child messages
I have a Linq query that looks something like this:
var query = from x in table where SomeFunctionReturnsBool() select;
private bool SomeFunctionReturnsBool()
{
return true;
}
This returns and exception that says "SomeFunctionReturnsBool has no supported translation to SQL". I get that this is because it wants to treat "SomeFunctionReturnsBool" as an expression to evaluate as SQL, but it can't.
Although this Linq query isn't complicated, the real ones are. How can I accomplish what I'm trying to do here, which is to break out pieces of the query to hopefully make it more readable?
Jeff
UPDATE
Good answers. I am trying now to work with expressions instead, but this code gets me "cannot resolve method Where(lambda expression)":
var query = from x in table where SomeFunctionReturnsBool() select x;
private Expression<Func<EligibilityTempTable, bool>> SomeFunctionReturnsBool
{
return (x) => true;
}
Another way is to use Expression<Func<YourType, bool>> predicate...
var query = from x in table where SomeFunctionReturnsBool() select;
Edit: I don't usually do it the way I've shown above... I was just getting that from the code above. Here is the way I usually implement it. Because then you can tack on additional Enumerable methods or comment them out during debugging.
var results = table.Where(SomeFunctionReturnsBool())
.OrderBy(yt => yt.YourProperty)
//.Skip(pageCount * pageSize) //Just showing how you can easily comment out parts...
//.Take(pageSize)
.ToList(); //Finally executes the query...
private Expression<Func<YourType, boo>> SomeFunctionReturnsBool()
{
return (YourType yt) => yt.YourProperty.StartsWith("a")
&& yt.YourOtherProperty == true;
}
I prefer to use the PredicateBuilder which allows you to build an expression to be used in your Where...
You can do this in LINQ-to-SQL by creating a UDF mapped to the data-context; this involves writing TSQL, and use ctx.SomeFunctionblah(...).
The alternative is to work with expression trees - for example, it could be:
Expression<Func<Customer, bool>> SomeFunc() {
return c => true; // or whatever
}
and use .Where(SomeFunc()) - is that close enough? You can't use the query syntax in this case, but it gets the job done...
Added dodgy Where method to show how you might use it in query syntax. I don't suggest this is fantastic, but you might find it handy.
using System;
using System.Linq;
using System.Linq.Expressions;
static class Program
{
static void Main()
{
using (var ctx = new NorthwindDataContext())
{
ctx.Log = Console.Out;
// fluent API
var qry = ctx.Customers.Where(SomeFunc("a"));
Console.WriteLine(qry.Count());
// custom Where - purely for illustration
qry = from c in ctx.Customers
where SomeFunc("a")
select c;
Console.WriteLine(qry.Count());
}
}
static IQueryable<T> Where<T>(this IQueryable<T> query,
Func<T, Expression<Func<T, bool>>> predicate)
{
if(predicate==null) throw new ArgumentNullException("predicate");
return query.Where(predicate(default(T)));
}
static Expression<Func<Customer, bool>> SomeFunc(string arg)
{
return c => c.CompanyName.Contains(arg);
}
}
Basically, "out of the box", you can't have LINQ-to-SQL execute queries that have custom functions in them. In fact only some native methods that can be translated to SQL can be used.
The easiest way around this can unfortunately affect performance depending on how much data you're bringing back from the DB.
Basically, you can only use custom functions in WHERE statments if the data has already been loaded into memory, i.e, SQL have already executed.
The quickest fix for your example would look like this:
var query = from x in table.ToList() where SomeFunctionReturnsBool() select;
Notice the ToList(). It executes the SQL and puts the data into memory. You can now do whatever you want in the WHERE statement/method.
I would just break them out like so:
Expression<Func<Table, bool>> someTreeThatReturnsBool = x => true;
var query = from x in table where someTreeThatReturnsBool select x;
You could create functions that pass around expression trees.
Don't use query syntax for this.
var query = table.Where( x => SomeFunction(x) );
I have this:
var sortName = Request.Params["sortName"];
var query = Request.Params["query"];
Func<UsuarioEndereco, bool> whereClause = (uen => uen.GetPropValue<string>(sortName).Contains(query));
The "uen.GetPropValue<string>(sortName)" will be filled dynamically with the sortName the user typed in the page.
For example, if an user looks for a person named "Joe", the snippet will be:
(uen => uen.namePerson.Contains(Joe))
But, I'm having problems with LINQ Case-sensitive searches. If I type "Joe", I will something. On the other hand, If I type "joe", it bring nothing.
How can I make this "Contains(sortName)" works with Case-Insensitive?? I've tried some things with String.Comparer but it reports errors on build solution.
Thanks!!
I believe the following will generate proper SQL:
uen=>(uen.GetPropValue<string>(sortName)).ToLower().Contains(query.ToLower()))
If this is really LINQ-to-SQL, try using the SqlMethods.Like method instead of String.Contains.
However, I think the problem is that this is NOT LINQ-to-SQL, because you are using delegates instead of Expression trees. So this is being brought client side, then executed locally ("LINQ to Objects"). Hence, String.Contains is doing what it does locally.
In that way, James's answer is correct, since he's calling ToLower() on both the value and the query. (Although, beware of culture issues -- perhaps specify which culture you want.)
You could also use the String.IndexOf Method (String, Int32, StringComparison) (http://msdn.microsoft.com/en-us/library/ms224424.aspx). This method allows you to specify if the matching should be done case-sensitively or not, and if it should use a Invariant culture or not.
So in your example:
Func<UsuarioEndereco, bool> whereClause = (uen => uen.GetPropValue<string>(sortName).IndexOf(query, 0, StringComparison.OrdinalIgnoreCase));
I'm not commenting on if this is a better solution than the one provided by James Curran. It could or could not be, performance wise.
This is the entire code:
var sortOrder = Request.Params["sortorder"];
var sortName = Request.Params["sortname"];
var query = Request.Params["query"];
IEnumerable<UsuarioEndereco> pagedEndereco;
Func<UsuarioEndereco, bool> whereClause = (uen => uen.GetPropValue<string>(sortName).Contains(query));
pagedEndereco = sortOrder.Equals("asc", StringComparison.CurrentCultureIgnoreCase) ?
_agendaServico.SelecionaUsuarioEnderecos(u.codUsuario).Where(whereClause).OrderByDescending(uen => uen.GetPropValue<IComparable>(sortName)) :
_agendaServico.SelecionaUsuarioEnderecos(u.codUsuario).Where(whereClause).OrderBy(uen => uen.GetPropValue<IComparable>(sortName));
The Extension Method GetPropValue is:
public static T GetPropValue<T>(this object component, string propertyName)
{
return (T)TypeDescriptor.GetProperties(component)[propertyName].GetValue(component);
}