The code snippet below search allow the user to match a string against three fields in the table. If any of the fields match, the entry is included in the result. However, using Where to filter out the results is resulting in "the string must match all three fields" instead "the string can match any of the three fields".
Is there a way to simulate an OrWhere expression when building LINQ queries dynamically?
var foundUsers = from UserInfo user in entities.UserInfo
select user;
if (searchCompleteName)
{
foundUsers = foundUsers.Where(u => u.CompleteName.Contains(searchString));
}
if (searchPortalID)
{
foundUsers = foundUsers.Where(u => u.PortalID.Contains(searchString));
}
if (searchUsername)
{
foundUsers = foundUsers.Where(u => u.UserIdentity.Contains(searchString));
}
PS. I am using Entities Framework and LINQ to Entities, and am doing a MVC3 Web Application.
Try this:- http://www.albahari.com/nutshell/predicatebuilder.aspx
Not exactly pretty, but it would work.
var foundUsers = entities.UserInfo.Where(u =>
(searchCompleteName && u.CompleteName.Contains(searchString))
|| (searchPortalID && u.PortalID.Contains(searchString))
|| (searchUsername && u.UserIdentity.Contains(searchString));
You could also do this with a union. The union operator returns distinct results so there will not be any duplicates. I have no idea if EF can defer this to the database.
var foundUsers = Enumerable.Empty<UserInfo>().AsQueryable();
if (searchCompleteName)
{
foundUsers = foundUsers.Union(entities.UserInfo.Where(u => u.CompleteName.Contains(searchString)));
}
if (searchPortalID)
{
foundUsers = foundUsers.Union(entities.UserInfo.Where(u => u.PortalID.Contains(searchString)));
}
if (searchUsername)
{
foundUsers = foundUsers.Union(entities.UserInfo.Where(u => u.PortalID.Contains(searchString)));
}
Related
Problem
I have an IQueryable, and I want to search it based on roles. An user can have multiple roles so I want to be able to add multiple search conditions (one on top of another).
public void OnGet()
{
var productionUnits = _context.ProductionUnits;
IQueryable query = productionUnits;
if (User.IsInRole(CustomRole.AdministratorUAP1))
{
query = productionUnits.Where(c => c.Id == (int)ProductionUnitEnum.UAP1);
}
if (User.IsInRole(CustomRole.AdministratorUAP2))
{
query = productionUnits.Where(c => c.Id == (int)ProductionUnitEnum.UAP2);
}
...
}
Expected Output
If the user is in multiple roles, for example UAP1 and UAP2, I want the query to get both of them in the Where clause. Is there any way to achieve this (I know I could do List.AddRange(), but I really want to update the query instead). Is there any way to achieve this?
I would creeate a list of roles for the user and use Contains in the query:
var roleIds = new List<int>();
if (User.IsInRole(CustomRole.AdministratorUAP1))
{
roleIds.Add(ProductionUnitEnum.UAP1);
}
if (User.IsInRole(CustomRole.AdministratorUAP2))
{
roleIds.Add(ProductionUnitEnum.UAP2)
}
var query = productionUnits.Where(c => roleIds.Contains(c.Id));
That will add an IN clause to your query for those two roles. If you have more than two roles just add them to the list as appropriate.
Each Linq function returns an IQueryable<>, so just keep reusing that:
IQueryable<T> query = productionUnits; // note the <T>
if (User.IsInRole(CustomRole.AdministratorUAP1))
query = query.Where(c => c.Id == (int)ProductionUnitEnum.UAP1);
if (User.IsInRole(CustomRole.AdministratorUAP2))
query = query.Where(c => c.Id == (int)ProductionUnitEnum.UAP2);
If the user is in multiple roles, for example UAP1 and UAP2
Then your database is fundamentally broken, you're checking those values against a single field: c.Id. One number can't be both values at the same time.
I've looked at the various solutions here but none of them seem to work for me, probably because I'm too new to all this and am groping in the dark a bit. In the code below, the object "appointment" contains some basic LDAP information. From a list of such objects I want to be able to get a single record, based on employee id. I hope the code here is sufficient to illustrate. FTR, I've tried various formulations, including trying to use from and a select. All fail with the error given in the Title above.
IQueryable<appointment> query = null;
foreach(var record in results)
{
BoiseStateLdapDataObject record1 = record;
query = db.appointments.Where(x => x.student_id == record1.Values["employeeid"]);
}
if (query != null)
{
var selectedRecord = query.SingleOrDefault();
}
Try to move employee id getting out of query:
IQueryable<appointment> query = null;
foreach(var record in results)
{
var employeeId = record.Values["employeeid"];
query = db.appointments.Where(x => x.student_id == employeeId);
}
if (query != null)
{
var selectedRecord = query.SingleOrDefault();
}
Is it possible ...??? I have 4 DropDownLists on my main page and the
user may select from any, all or some of
the DropDownLists. I am capturing their selection (or non-selection) using a SESSION
variable. What I would like to be able to do is pass the session
variable values to my Data Access Layer and build a WHERE clause
(maybe using StringBuilder) and then place that variable SOMEHOW into
my query expression. Is that possible??? Sorry, I'm a newbie. Thanks ~susan~
public class DLgetRestaurants
{
FVTCEntities db = new FVTCEntities();
public List<RESTAURANT> getRestaurants(string cuisineName, string priceName, string cityName)
[Build a string based on the values passed to the function]
{
var cuisineID = db.CUISINEs.First(s => s.CUISINE_NAME == cuisineName).CUISINE_ID;
List<RESTAURANT> result = (from RESTAURANT in db.RESTAURANTs.Include("CITY").Include("CUISINE").Include("Price")
where **[USE STRINGBUIDER EXPRSSION HERE]**
select RESTAURANT).ToList();
return result;
}
}
You can compose Where conditions which are linked by a logical AND relatively easy in LINQ extension method syntax:
var query = db.RESTAURANTs.Include("CITY").Include("CUISINE").Include("Price");
if (userHasSelectedInDDL1)
query = query.Where(r => r.PropertyForDDL1 == ValueFromDDL1);
if (userHasSelectedInDDL2)
query = query.Where(r => r.PropertyForDDL2 == ValueFromDDL2);
if (userHasSelectedInDDL3)
query = query.Where(r => r.PropertyForDDL3 == ValueFromDDL3);
if (userHasSelectedInDDL4)
query = query.Where(r => r.PropertyForDDL4 == ValueFromDDL4);
List<RESTAURANT> result = query.ToList();
For a much more flexible solution to build queries dynamically the Dynamic LINQ Library recommended by boca is probably the better choice.
I have done this in the past using the Dynamic Linq Library.
This is a follow up on a related topic found here
https://stackoverflow.com/questions/1987485/conditionally-assign-c-var-as-elegant-as-it-gets
if I am doing the following:
var query = (SearchString == "" ?
(
from MEDIA in xdoc.Descendants("MEDIA")
select new
{
PLAY = MEDIA.Element("PLAY").Value,
PIC = MEDIA.Element("PIC").Value,
TTL = MEDIA.Element("TTL").Value
}
):
from MEDIA in xdoc.Descendants("MEDIA")
where MEDIA.Element("TTL").ToString().ToLower().Contains(SearchString)
select new
{
PLAY = MEDIA.Element("PLAY").Value,
PIC = MEDIA.Element("PIC").Value,
TTL = MEDIA.Element("TTL").Value
}
) ;
How would I declare the query type to make it static at the class level?
Alternatively, in the referenced post Marc Gravell point out a different approach
IQueryable<Part> query = db.Participant;
if(email != null) query = query.Where(p => p.EmailAddress == email);
if(seqNr != null) query = query.Where(p => p.SequenceNumber == seqNr);
...
How would I declare/recode the query in my case?
Here is my wild attempts :)
IEnumerable<XElement> query = xdoc.Descendants("MEDIA");
if (SearchString != "" )
query = query.Where(m => m.Element("TTL").ToString().ToLower().Contains(SearchString));
Thank you.
How would I declare the query type to make it static at the class level?
You can't. Anonymous types are, well, anonymous... so they don't have a name you can use to declare variables. Your query is of type IEnumerable<something>, but you can't refer to something in your code. So you need to create a specific class that represent the results of your query, and use it instead of the anonymous type.
I have a variable size array of strings, and I am trying to programatically loop through the array and match all the rows in a table where the column "Tags" contains at least one of the strings in the array. Here is some pseudo code:
IQueryable<Songs> allSongMatches = musicDb.Songs; // all rows in the table
I can easily query this table filtering on a fixed set of strings, like this:
allSongMatches=allSongMatches.Where(SongsVar => SongsVar.Tags.Contains("foo1") || SongsVar.Tags.Contains("foo2") || SongsVar.Tags.Contains("foo3"));
However, this does not work (I get the following error: "A lambda expression with a statement body cannot be converted to an expression tree")
allSongMatches = allSongMatches.Where(SongsVar =>
{
bool retVal = false;
foreach(string str in strArray)
{
retVal = retVal || SongsVar.Tags.Contains(str);
}
return retVal;
});
Can anybody show me the correct strategy to accomplish this? I am still new to the world of LINQ :-)
You can use the PredicateBuilder class:
var searchPredicate = PredicateBuilder.False<Songs>();
foreach(string str in strArray)
{
var closureVariable = str; // See the link below for the reason
searchPredicate =
searchPredicate.Or(SongsVar => SongsVar.Tags.Contains(closureVariable));
}
var allSongMatches = db.Songs.Where(searchPredicate);
LinqToSql strange behaviour
I recently created an extension method for creating string searches that also allows for OR searches. Blogged about here
I also created it as a nuget package that you can install:
http://www.nuget.org/packages/NinjaNye.SearchExtensions/
Once installed you will be able to do the following
var result = db.Songs.Search(s => s.Tags, strArray);
If you want to create your own version to allow the above, you will need to do the following:
public static class QueryableExtensions
{
public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> stringProperty, params string[] searchTerms)
{
if (!searchTerms.Any())
{
return source;
}
Expression orExpression = null;
foreach (var searchTerm in searchTerms)
{
//Create expression to represent x.[property].Contains(searchTerm)
var searchTermExpression = Expression.Constant(searchTerm);
var containsExpression = BuildContainsExpression(stringProperty, searchTermExpression);
orExpression = BuildOrExpression(orExpression, containsExpression);
}
var completeExpression = Expression.Lambda<Func<T, bool>>(orExpression, stringProperty.Parameters);
return source.Where(completeExpression);
}
private static Expression BuildOrExpression(Expression existingExpression, Expression expressionToAdd)
{
if (existingExpression == null)
{
return expressionToAdd;
}
//Build 'OR' expression for each property
return Expression.OrElse(existingExpression, expressionToAdd);
}
}
Alternatively, take a look at the github project for NinjaNye.SearchExtensions as this has other options and has been refactored somewhat to allow other combinations
There is another, somewhat easier method that will accomplish this. ScottGu's blog details a dynamic linq library that I've found very helpful in the past. Essentially, it generates the query from a string you pass in. Here's a sample of the code you'd write:
Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products _
.Where("CategoryID=2 AND UnitPrice>3") _
.OrderBy("SupplierId")
Gridview1.DataSource = query
Gridview1.DataBind()
More info can be found at scottgu's blog here.
Either build an Expression<T> yourself, or look at a different route.
Assuming possibleTags is a collection of tags, you can make use of a closure and a join to find matches. This should find any songs with at least one tag in possibleTags:
allSongMatches = allSongMatches.Where(s => (select t from s.Tags
join tt from possibleTags
on t == tt
select t).Count() > 0)