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 :)
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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.
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 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) )
This seems to be about the most generic error I've come across - multiple SO posts about it are all referring to different issues - well here's a new one :)
I get the error above when the following IQueryable is enumerated:
N.B. items is an IQueryable<tblItem> and keywords is a string
items = items.Where(p => p.heading.ToLower().Contains(keywords) ||
p.description.ToLower().Contains(keywords));
This is confusing because, as the error suggests, it should work fine when you use a Contains - does anyone know how to fix this?
If keyword is a collection that supports enumeration, then it should be other way around:
items = items.Where(p => keywords.Contains(p.heading.ToLower()) ||
keywords.Contains(p.description.ToLower()));
If items is IQueryable then the error may be there and nothing to do with your where statement.
Can you try forcing enumeration before adding your where statement?
For example, suppose you are attempting to join an in memory list with a datatable you will get that error when the query is evaluated or enumerated
List<tblCategory> categories = tblCategory.ToList();
IQueryable<tblItem> items = (from r in tblItem
join c in categories on r.CategoryID equals c.Id select r);
// items = items.Where(p => p.heading.ToLower().Contains(keywords) ||
// p.description.ToLower().Contains(keywords));
var firstMatch = items.FirstOrDefault();
// The error will be generated here even if the where is remmed out
SOLVED
Thanks sgmoore for your input - it helped arrive at this solution:
Assgning the IQueryable list to an IEnumerable list, running a ToList on it and THEN using my filters on the list worked great.
IEnumerable<tblItems> temp = items.ToList();
temp = temp.Where(p => p.heading.ToLower().Contains(keywords) ||
p.description.ToLower().Contains(keywords));
items = temp.AsQueryable();
Linq Select method takes Func as input parameter. This means I can have multiple statements in selector for Select, such as
var myresult = sources.Select(s =>
{int x; if (s.val = high) {x=1} else if (s.val = med) {x=2} else {x=3}; return x;
}
)
How can I do this using Linq query syntax
var myresult = from s in sources
select ...
Here, the code in Func part (if ... else if .. else) is artificial. What I really want to know is the syntax of select clause, which may be described as
select select-expression
What is the syntax of
select-expression
I wouldn't want to see your first version in my code. If you need to have what is basically a full function in the lambda, I would rather see the lambda simply invoke a full function! In other words...
theQuery.Select(s => GetX(s)); // just define a GetX function
And that would also be a straightforward translation to query expression syntax
from s in sources
select GetX(s);
You would not be able to put your full code block into the query expression syntax. You could translate your given logic to something usable (yet messy), however I'm quite sure your snippet is just a general example. On the offhand change it isn't, you might try
select s.val == high ? 1 : (s.val == med ? 2 : 3); // totally messy
Instead of special-casing values, with the if/else equivalent of a switch statement, it is more Linq-friendly to group and filter your values:
var myResult = from s in sources
group by s.val into g
select new { Val = g.Key, Sources = g };
var groupHigh = myResult.Where(i => i.Val == high);
var groupMedium = myResult.Where(i => i.Val == medium);
var groupOther = myResult.Except(groupHigh.Concat(groupMedium));
Note that the code I've provided is just a starting place, and isn't the best way to achieve your specific goal. I'd address this in one of these ways:
Change how group by is used (use SomeFunction(s.Val) instead of directly using s.Val)
Change the code around this query to flow better with the natural groupings, so I didn't require the groups to be transformed
This is not possible.
If you really want to, you could create an Func<T> from an anonymous method and invoke it, but that would be horrible.
MSDN indicates select is a contextual keyword of C# 4.0. So I checked the C# Language Specififcation 4.0. Its Select clauses section (7.16.2.5) specifies that
A query expression of the form
from x in e select v
is translated into
( e ) . Select ( x => v )
except when v is the identifier x, the translation is simply
( e )
As the result, the syntax for
select select-expresion
select-expression should be anything that can be used as TResult in Select Method. So the functionality can be done using anonymous Func in Select method may not be able to achieved using select clause.
Conclusion is that you should stick with Method syntax as this is how the code really runs behind the scene.
I'm trying to merge these two object but not totally sure how.. Can you help me merge these two result objects?
//
// Create Linq Query for all segments in "CognosSecurity"
//
var userListAuthoritative = (from c in ctx.CognosSecurities
where (c.SecurityType == 1 || c.SecurityType == 2)
select new {c.SecurityType, c.LoginName , c.SecurityName}).Distinct();
//
// Create Linq Query for all segments in "CognosSecurity"
//
var userListAuthoritative3 = (from c in ctx.CognosSecurities
where c.SecurityType == 3 || c.SecurityType == 0
select new {c.SecurityType , c.LoginName }).Distinct();
I think I see where to go with this... but to answer the question the types of the objects are int, string, string for SecurityType, LoginName , and SecurityName respectively
If you're wondering why I have them broken like this is because I want to ignore one column when doing a distinct. Here are the SQL queries that I'm converting to SQL.
select distinct SecurityType, LoginName, 'Segment'+'-'+SecurityName
FROM [NFPDW].[dbo].[CognosSecurity]
where SecurityType =1
select distinct SecurityType, LoginName, 'Business Line'+'-'+SecurityName
FROM [NFPDW].[dbo].[CognosSecurity]
where SecurityType =2
select distinct SecurityType, LoginName, SecurityName
FROM [NFPDW].[dbo].[CognosSecurity]
where SecurityType in (1,2)
You can't join these because the types are different (first has 3 properties in the resulting type, second has two).
If you can tolerate putting a null value in for the 3rd result of the second query this will help. I would then suggest you just do a userListAuthoritative.concat(userListAuthoritative3 ) BUT I think this will not work as the anonymous types generated by the linq will not be of the same class, even tho the structure is the same. To solve that you can either define a CustomType to encapsulate the tuple and do select new CustomType{ ... } in both queries or postprocess the results using select() in a similar fashion.
Acutally the latter select() approach will also allow you to solve the parameter count mismatch by implementing the select with a null in the post-process to CustomType.
EDIT: According to the comment below once the structures are the same the anonymous types will be the same.
I assume that you want to keep the results distinct:
var merged = userListAuthoritative.Concat(userListAuthoritative3).Distinct();
And, as Mike Q pointed out, you need to make sure that your types match, either by giving the anonymous types the same signature, or by creating your own POCO class specifically for this purpose.
Edit
If I understand your edit, you want your Distinct to ignore the SecurityName column. Is that correct?
var userListAuthoritative = from c in ctx.CognosSecurities
where new[]{0,1,2,3}.Contains(c.SecurityType)
group new {c.SecurityType, c.LoginName, c.SecurityName}
by new {c.SecurityType, c.LoginName}
select g.FirstOrDefault();
I'm not exactly sure what you mean by merge, since you're returning different (anonymous) types from each one. Is there a reason the following doesn't work for you?
var userListAuthoritative = (from c in ctx.CognosSecurities
where (c.SecurityType == 1 || c.SecurityType == 2 || c.SecurityType == 3 || c.SecurityType == 0)
select new {c.SecurityType, c.LoginName , c.SecurityName}).Distinct();
Edit: This assumed they were of the same type -- but they're not.
userListAuthoritative.Concat(userListAuthoritative3);
Try below code, you might need to implement IEqualityComparer<T> in your ctx type.
var merged = userListAuthoritative.Union(userListAuthoritative3);