I get the following error when trying to run a specific query against RavenDB:
Can't extract value from expression of type: ArrayIndex
Here is the query that is generating the error:
people = from p in RavenSession.Query<DBObjects.Person, People_ByNameAndTrashedSortByFirstNameAndLastName>()
orderby p.FirstName, p.LastName
select p;
...
//building LINQ query
...
people = from p in people
where ((p.FirstName.StartsWith(SearchWords[0])) && (p.LastName.StartsWith(SearchWords[1])))
select p;
...
//later
foreach(DBObject.Person person in people) //triggers error listed above
{
}
I'm wondering if this is a limitation of RavenDB. I noticed that if I switch && with ||, then I get no error. Of course, I don't get the results I want either. I've also tried rewriting the query as:
people = from p in people
where p.FirstName.StartsWith(SearchWords[0])
where p.LastName.StartsWith(SearchWords[1])
select p;
I get the same error.
I've also tried using a dynamic index instead of a static index. I get the same error.
I suppose maybe RavenDB LINQ driver cannot cope with extracting value from array inside the query. Try to put already extracted values in the place of SearchWords[0] and SearchWords[1] instead:
var pref1 = SearchWords[0];
var pref2 = SearchWords[1];
... where ( p.FirstName.StartsWith(pref1) && p.LastName.StartsWith(pref2) )
Related
I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));
I am trying to return the results of a query into a List object, however the following code, as I normally use, does not work. Still relatively new to Linq, can someone explain the correct syntax/what's going on? This will work if I change the data type of productTraining to var...
List<AgentProductTraining> productTraining = new List<AgentProductTraining>();
productTraining = from records in db.CourseToProduct
where records.CourseCode == course.CourseCode
select records;
Select() and Where() will return IQueryable<T>, not List<T>. You've got to convert it to a List<T> - which actually executes the query (instead of just preparing it).
You just need to call ToList() at the end of the query. For example:
// There's no need to declare the variable separately...
List<AgentProductTraining> productTraining = (from records in db.CourseToProduct
where records.CourseCode == course.CourseCode
select records).ToList();
Personally I wouldn't use a query expression though, when all you're doing is a single Where clause:
// Changed to var just for convenience - the type is still List<AgentProductTraining>
var productTraining = db.CourseToProduct
.Where(records => records.CourseCode == course.CourseCode)
.ToList();
I am having some trouble with a linq query I am trying to write.
I have List A of products that have been modified so I am trying to get the list of products from the db to allow me to apply the changes to them.
I have tried 2 different queries
var query = from p in db.Products
where products.Select(z => z.id).Contains(p.Id)
select p;
var query2 = from p in db.Products where (from o in products
select o.id)
.Contains(p.Id)
select p;
Both attempts are returning an error
base {System.SystemException} = {"Unable to create a constant value of type 'ProjectABC.Models.ProductModel'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."}
What am I doing wrong?
I had the same problem the other day, seems EF doesn't support Select().Contains() without giving that error. After testing around for a bit, I ended up splitting it up in what in your case would correspond to;
var IDs = products.Select(z=>z.id);
var query = from p in db.Products
where IDs.Contains(p.Id)
select p;
which worked well in my case when the "products" collection was in memory anyway (ie a ToList()'ed result from the database)
I'm programming a search for a SQLite-database using C# and LINQ.
The idea of the search is, that you can provide one or more keywords, any of which must be contained in any of several column-entries for that row to be added to the results.
The implementation consists of several linq-queries which are all put together by union. More keywords and columns that have to be considered result in a more complicated query that way. This can lead to SQL-code, which is to long for the SQLite-parser.
Here is some sample code to illustrate:
IQueryable<Reference> query = null;
if (searchAuthor)
foreach (string w in words)
{
string word = w;
var result = from r in _dbConnection.GetTable<Reference>()
where r.ReferenceAuthor.Any(a => a.Person.LastName.Contains(word) || a.Person.FirstName.Contains(word))
orderby r.Title
select r;
query = query == null ? result : query.Union(result);
}
if (searchTitle)
foreach (string word in words)
{
var result = from r in _dbConnection.GetTable<Reference>()
where r.Title.Contains(word)
orderby r.Title
select r;
query = query == null ? result : query.Union(result);
}
//...
Is there a way to structure the query in a way that results in more compact SQL?
I tried to force the creation of smaller SQL-statments by calling GetEnumerator() on the query after every loop. But apparently Union() doesn't operate on data, but on the underlying LINQ/SQL statement, so I was generating to long statements regardless.
The only solution I can think of right now, is to really gather the data after every "sub-query" and doing a union on the actual data and not in the statement. Any ideas?
For something like that, you might want to use a PredicateBuilder, as shown in the chosen answer to this question.
I'm trying to wrap my head around linq -> nhib
I have a simple bit of sql that i'm trying to get working in nhibernate.linq
select * from
ColModel where ColModel.DataIndex
not in ('CostElement1', 'CostElement2', 'CostElement3')
and ColModel.ReportId = 1
The list of excluded DataIndex values comes in in the form of a List<string> called excludeNames
Here is what I have tried but it seems that it's not really feeling the love:
var s = base._sessionManager.OpenSession();
var query = from col in s.Linq<ColModel>()
where col.Report.Id == reportid &&
!(from c in s.Linq<ColModel>() select c.DataIndex).Contains(excludeNames)
select col;
return query.ToList();
the error:
The type arguments for method 'System.Linq.Enumerable.Contains<TSource>(System.Collections.Generic.IEnumerable<TSource>, TSource)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
I'm pretty sure I'm borfing this from the offset so any pointers would be well appreciated :)
w://
Contains doesn't accept a list.
There are ways to work around this in LINQ, but I'm not sure which, if any, of those will work in NH Linq
I think you have your exclusion backwards.
s = base._sessionManager.OpenSession();
var query = from col in s.Linq<ColModel>()
where col.Report.Id == reportid &&
!excludeNames.Contains(col.DataIndex)
select col;
return query.ToList();
Collection.Contains(item) will produce the SQL item in (...collection...), adding the negation will get you what you want.