I have this Lookup to group ResultId by Symbol.
I have Linq query below but I cannot make SQL IN statement by using Contain() which is state by this post http://blog.wekeroad.com/2008/02/27/creating-in-queries-with-linq-to-sql
// This will group ResultIds (Guid) by their symbol (string).
var asd = ResultIdsAndSymbols.ToLookup(x => x.Symbol, y => y.ResultID);
foreach (var qwe in asd)
{
var Numbers = (from t in Session.Query<TableName>()
where qwe.Contains(t.ResultID)
select t.Number).ToList();
}
Update:
After retrying this code and deep analyzing the error (System.InvalidCastException: Object must implement IConvertible), I got this informative error message: "Failed to convert parameter value from a Grouping to a Guid". qwe is a type of IGrouping<string, Guid> and it will become IEnumerable<Guid> which should not be a problem like we pass this into a List constructor or used in foreach statement. The exception thrown in System.Data.SqlClient. I think NHibernate simply pass the Grouping<TKey, TElement> into the sql parameter that cause the error. NHibernate should be designed to enumerate to any IEnumerable<T> and generate the SQL IN query just like how it does for List<T>.
The List<T>, Array[], Stack work well. So I change the code to this:
where qwe.ToList().Contains(t.ResultID)
Update:
Issue reported: https://nhibernate.jira.com/browse/NH-2762
The NHibernate LINQ provider is limited when it comes to the IN clause. It seems to only work with collections where T is a simple type, e.g. List<string> or List<int>.
This works in NHibernate 3.1 (not tested in earlier versions):
var asd = ResultIdsAndSymbols.ToLookup(x => x.Symbol, y => y.ResultID);
foreach (var qwe in asd)
{
List<int> list = qwe.ToList();
var Numbers = (from t in Session.Query<TableName>()
where list.Contains(t.ResultID)
select t.Number).ToList();
}
Related
In C# you can group by .Date:
db.History.GroupBy(x => x.Timestamp.Date)
.Select(g => new { key = g.Key, aggregate = g.Count() })
However, the equivalent F# does not work:
db.History.GroupBy(fun x -> x.Timestamp.Date)
.Select(fun g -> { Date = g.Key; Count = g.Count()} )
The relevant record:
type DateCount = {
Date: DateTime
Count: int
}
It throws the following error:
System.InvalidOperationException: The LINQ expression 'DbSet<HistoryEntity>
.GroupBy(
source: h => copyOfStruct => copyOfStruct.Date.Invoke(h.Timestamp),
keySelector: h => h)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync().
How can I group by date?
So in C#, when you use LINQ-to-SQL queries, you are using the extension methods on IQueryable<T>. If we look at the signature of say, the GroupBy method, you will see that the function signature is actually
IQueryable<TSource>.GroupBy<TSource,TKey>(Expression<Func<TSource,TKey>> keySelector)
What's going on? Expression<> is a special type - when the C# compiler spots an Expression<> type, the compiler builds an AST, and passes the AST object (of type Expression<Func<>>), instead of the usual delegate. The underlying functions are expected to inspect the AST and build whatever query expression is finally needed, like SQL for querying the database.
You can try it yourself:
Expression<Func<int>> getRandom = () => 4; //random, chosen by fair dice roll
You can inspect the properties of getRandom to see the AST.
Since the magic happens in the C# compiler, when you do it in F#, this won't cut it.
To go into more detail, the F# compiler can recognize the Expression<>, but it does so by applying an implicit F# quotation - so you get an F# quotation wrapped method call that translates to the C# expression tree. (Sorry if, that was run on.)
F# has its own query comprehension builder for SQL. It lets you write the computation expressions like that of seq which translate to SQL queries. This works like you'd expect.
query {
for record in db do
select record
}
Group by .Date works when using in a query expression.
query {
for h in db.History do
groupValBy h h.Timestamp.Date into g
select {
Date = g.Key
Count = g.Count()
}
}
Code stolen from here.
If someone could explain why the query expression works but the LINQ version doesn't, I'd appreciate it :)
I want to get list of records from an entity model (I'm using EF version 5) with a particular accountID. I'm being supplied with the tableName string (this has to be dynamic) and the accountID. I'm trying the following 2 methods but none of them is working (giving me errors on the IQueryable object 'table':
PropertyInfo info = _db.GetType().GetProperty(tableName);
IQueryable table = info.GetValue(_db, null) as IQueryable;
var query = table.Where(t => t.AccountID == accID)
.Select(t => t);
List <object> recList = ( from records in table
where records.AccountID == accID
select records).ToList<object>();
The var query = table.Where(....).Select(...) is the correct move as it allows reflection for the query builder at runtime. However, t.AccountID is an error because of the type of t remains unknown.
I've previously used a similar approach in LINQ to SQL, using System.Linq.Expressions.Expression, e.g.:
// NOT TESTED
var table=context.GetTable(dynamicTableName);
var theT=table.Experssion; // actually, I forget. DynamicExpression or MemberBinding? or
var theField=Expression.Field(theT, "AccountID"); // or dynamic name
var query=table.Where(Expression.Equal(theField, accID);
var recList=query.ToList<object>();
If your object has a common interface there is a simpler syntax:
IQueryable<MyInterface> table = context.GetTable("table") as IQueryable<MyInterface>;
var recList=from r in table
where table.AccountID == ac // if your AccountID is on MyInterface
select table;
If you only have a few tables to support, you could do this as well:
IQueryable<MyInterface> table;
if("table1"==tableName)
table=_db.table1
elseif("table2"==tableName)
table=_db.table2
elseif("table3"==tableName)
table=_db.table3
else
throw exception
I built a DynamicRepository for a project I am working on. It uses generic methods exposed through EF along with dynamic linq. It might be helpful to look at that source code here:
https://dynamicmvc.codeplex.com/SourceControl/latest#DynamicMVC/DynamicMVC/Data/DynamicRepository.cs
You can query the entity framework metadata workspace to get the type for a given table name. This link might help:
Get Tables and Relationships
I've got an entity called new_trexmail with a string attribute called new_contextline.
I'm trying to get a list of entities where new_contextlineis in a defined list.
The following code fails with the error : NotSupportedException: Invalid 'where' condition. An entity member is invoking an invalid property or method.
string[] test = new[]{"aaa", "hhh"};
var query = from n in New_trexmailSet
where test.Contains(n.New_contextline)
select n;
I understand why this error is being thrown but I'm wondering if it's possible to do the equiavalent of an IN clause using XRM.
If it is possible then how do I go about getting XRM to execute SELECT * FROM new_trexmail WHERE new_contextline in ('aaa', 'hhh')?
Thanks,
David
Check out the (longer than desired) list of LINQ limitations, particularly the limitation on the where clause:
The left side of the clause must be an attribute name and the right
side of the clause must be a value. You cannot set the left side to a
constant. Both the sides of the clause cannot be constants. Supports
the String functions Contains, StartsWith, EndsWith, and Equals.
So since test isn't a CRM attribute, you can't call Contains on it. However, one way around this is to use "Dynamic Linq" as developed by ScottGu and as demonstrated below:
//must include the below using statements
//using System.Linq;
//using System.Linq.Dynamic;
var trexmailSet = New_trexmailSet;
string[] test = new[] { "aaa", "hhh" };
string whereClause = "";
foreach (string name in test)
{
whereClause += string.Format("new_contextline = \"{0}\" OR ", name);
}
trexmailSet = trexmailSet.Where(whereClause.Substring(0, whereClause.Length - 4));
var query = from n in trexmailSet
select n;
It's an exercise of EF code-first. There's a simple method. I want to get the Entity SQL command text generated by object services.
(MyDbContext is derived form DbContext. Person is a POCO class.)
using (MyDbContext context = new MyDbContext())
{
var query = context.Set<Person>().FirstOrDefault(p => p.Age == 1);
Console.WriteLine(query.Name);
var objquery = query as ObjectQuery;
if (objquery != null)
Console.WriteLine(objquery.CommandText);
}
I used to get native SQL command text by ObjectQuery.TraceString in LINQ to Entity. Now, what I need is Entity-SQL statement, NOT native SQL statement.
But, I can't cast the query from IQueryable<Person> to ObjectQuery or ObjectQuery<Person>.
I tried to get members of DbQuery by reflection. It seems that DbQuery hasn't any property about command text or trace string.
Thanks
My suggestion for what you want is using Dynamic Linq. The library (part of the Linq Samples) includes many IQueryable extensions that return Linq.DataQuery objects. Once you consume the DataQuery you'll have the expected object.
var testQuery =
db.Cases.
Where("KeyID > 1").
Take(1);
foreach (var r in testQuery)
{
Console.WriteLine(r);
}
Then, you can check against your query as such.
testQuery.Expression
testQuery.Provider
These will give you:
{Table(Case).Where( => (.Keyid > 1)).Take(1)}
System.Linq.Expressions.Expression {System.Linq.Expressions.MethodCallExpression}
-and-
{SELECT TOP (1) [t0].[Keyid], [t0].[FileNo], [t0].[MatterType], [t0].[LoanNo], [t0].[Investor], [t0].[LoanType], [t0].[Client], [t0].[ClientFileNo], [t0].[ClientStatus], [t0].[Mortgagor], [t0].[County], [t0].[PropertyStreet1], [t0].[PropertyStreet2], [t0].[PropertyCity], [t0].[PropertyState], [t0].[PropertyZipcode], [t0].[Status], [t0].[BoxNo], [t0].[InsurerLoanno], [t0].[InvestorLoanno], [t0].[insurer_name_id], [t0].[OldSystemKey], [t0].[FinalBilling], [t0].[HoldBilling], [t0].[LastModified], [t0].[PiggyLoanNo], [t0].[CurrComentID], [t0].[LockEFILE], [t0].[MSJAmount], [t0].[Created], [t0].[Locked], [t0].[FinalBillingDate], [t0].[HoldBillingDate], [t0].[CreatedBy], [t0].[Stage], [t0].[PriorStage], [t0].[DefendantUpdated], [t0].[VestingCode], [t0].[FileSource], [t0].[SubVestingCode], [t0].[AttorneyAssigment], [t0].[VoluntarySurrender], [t0].[FNMARisk], [t0].[Source], [t0].[REO_ID], [t0].[WTI_ID], [t0].[CaseDismissed], [t0].[REO_CompanyID], [t0].[SubMattertype], [t0].[VendorCode], [t0].[SubType]
FROM [dbo].[Cases] AS [t0]
WHERE [t0].[Keyid] > #p0}
System.Linq.IQueryProvider {System.Data.Linq.DataQuery<CMSDEVMapping.Case>}
You can also verify your type in the loop:
r.GetType() {Name = "Case" FullName = "CMSDEVMapping.Case"} System.Type {System.RuntimeType}
I've got a situation where I need to use a custom expression in a LINQ to Entities query (because I want to have custom logic that L2E wouldn't otherwise understand:
var query = db.MyTable.Where(MyPredicateExpression)
But I'd rather use query comprehension syntax:
var query = from x in db.MyTable where [x matches the predicate of MyPredicateExpression]
I know this is possible, because L2E supports it in other places:
var query = from x in db.MyTable where x.Length > 10
How do they make that work?
Edit: I'm using devart's LinqConnect for Oracle, which may behave somewhat differently than Microsoft L2E.
Entity Framework and LINQ to SQL do not support this scenario, because the translation of MyPredicateExpression should be added to expression tree translator.
I recommend you to create a stored function performing the predicate check and add this function to DataContext. You will be able to use a query like the following in this case:
var query = from x in db.MyTable where context.MyPredicateFunction(x.Field) select x;
Update. Here is the updated query that takes into account your comments:
int[] values = new int[] { 1, 2, 3 };
var query = from x in db.MyTable where values.Contains(x.AuditState) select x;
Update 2. You can add a Queryable property to your context that will be obtaining the necessary set of MyTable objects as shown in the following example:
public partial class MyDataContext {
IQueryable<MyTable> GetSpecialTables {
get {
int[] values = new int[] { 1, 2, 3 };
return this.MyTables.Where(x => values.Contains(x.AuditState));
}
}
}
Replace MyDataContext with the actual name of your context.
If I understand the problem correctly, you can either use an extension method OR call a function that returns a bool.