ADO.NET :: How To Use LINQ In Order To Filter Out Only Objects
Nov 24, 2010
I have a collection of objects that I want to use LINQ in order to filter out only objects that have properties that meet a certain criteria. I am not big on LINQ so I am not sure how to do this.
I create a basic LINQ statement and get the records this way
Dim lr As IEnumerable(Of LogRecord) = From rr In _logRecords where rr.username="something"
but I only want to add that where condition if someone actually filled in a textbox.
I have other conditions to do the same thing with.
I'm trying to use formview in order to do insert of a new entity object (called Customer) Customer has a reference to another entity called Address. How can I fill both of them in the same formview?
HTML Code: (From r In tblRoles Join m In module_master On m.module_id Equals r.module_id Where Not r.role_name.ToUpper.Contains("OWNER") And Not r.role_name.ToUpper.Contains("CLIENT") Order By m.module_name, r.role_name Select r.module_id, m.module_name ,r.role_name ).Distinct and output is
[code]....
but when i remove distinct then order by works properly..???
How do you reference a LINQ object that you have created such as a list, in your HTML? I have seen examples of how to do this using MVC, but I am using Web Forms. Here is my LINQ :
[Code]....
And I want to be able to for example check if my linq returns any data and if so iterate through it using a foreach loop in my HTML. change my linq so that it returns a generic list rather than what it is doing at the moment.
Private Sub MakeMeSomeXmlBeforeRyanGetsAngry() Dim db As New MyDBDataContext Dim customer = From c In db.Customers Select c Dim dcs As New DataContractSerializer(GetType(Customer)) Dim sb As StringBuilder = New StringBuilder Dim writer As XmlWriter = XmlWriter.Create(sb) dcs.WriteObject(writer, customer) Dim xml As String = sb.ToString Response.Write(xml) End Sub
I am attempting to serialize my linq collection of customers. But it keeps throwing
Type 'System.Data.Linq.DataQuery`1[MyDB.Customer]' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. See the Microsoft .NET Framework documentation for other supported types.
My issue is that I have already marked the dbml Serialization Mode to UniDirectional and when I check the dbml codebehind all of the DataContract()> and DataMember()> elements are there.
I am not sure how to proceed. I have tried adding various dataloadoptions and setting deferredloading to false, but no luck.
Many times I need to manipulate with DataTable after I get data from database using adapter.Fill(table).
Usually I calculate data in DataTable by using loops. But I know that there is simpler way using LINQ. I know some basics about that just for strongly typed objects.I can't find how to do this with DataTable that is not strongly typed. How could I get all DataRow or Filtered DataTable (not just value for the field) from table for that conditions:
- where the specified field of the table contans MAX/MIN/AVG value, - where the specified field of the table equals to some value.
I need to filter LINQ query using comboboxes and textboxes. The problem is I can't manage to get the result and I always get the empty gridview (used for showing filtered data). Can anyone help me why am I getting no results at all? I've checked the debugger and the data sent to query is valid, although, I'm not sure about "string.Empty" value.
I have an Entity class which has a Dictionary of fields called Data. Now I want to sort Entities by a field in Data. I was able to verify the Linq expression for using fields in a dictionary as e.Data["UserId"] as this seemed to work perfectly when I used LINQ to Objects. e.g. Entities.OrderBy(e => e.Data["UserId"])
However this same expression does not generate the correct NHibernate criteria and errors out finally with a NullReferenceException for propertyName at Hibernate.Loader.Criteria.CriteriaQueryTranslator.GetEntityName(ICriteria subcriteria, String propertyName)in CriteriaQueryTranslator.cs: line 541.
On debugging through NHibernate code, I figured that NHibernate.Linq.Visitors.MemberNameVisitor.GetMemberName(ICriteria rootCriteria, Expression expr) returns a null string in place of the field name after visiting expr using its visitor. This seems to be the cause of grief. I am using an older version of NHibernate (2.1). Are there any limitations in the NHibernate Linq visitor I should be aware of?
I am use the new ASP.NET MVC 2 and Entity Framework, but when I try to create a new view with strongly-typed option selected, the entity objects is not appears at dropdown and I cannot use the view creation wizard. I recompile the solution, but still not appears yet. Have any workaround that I forgot to do to enable the entities to be displayed at dropdownlist ?
I am using Linq To Sql to get List of objects with data from database. To bind data with a grid view i am creating a dataset explicitly and then adding List values to that explicitly created dataset.
Now my question is whether it is a good pratice to do what i am doing (in terms of resource utilization) or is there any better way to this...
I'm new on LINQ and I'm searching the best way to do this:
I have an object client that has a list of subscriptions. Subcription has a boolean attribute "Active". Now I want load only the clients with list > 0 and subscription active.
The question is: If a client has 3 subscriptions, but only 2 are active, how can I load only the latters ? I tried in this way:
[Code]....
The query selects clients that has at least one subscription active, but viewing the results, it loads also subscriptions not active of the same client.
I have two business objects mapped via LINQ to tables. One of the objects contains an instance of the other object and share a key as an identifier.I want to retrieve Class A and within class A all of Class B's values as well. What I am doing is this:
[Code]....
[Code]....
This seems a little clunky, as in slow. Is there a better way to get the Class B (User) information without making a query every time?
I have written a page which uses Linq to query the database and bind the resulting IQueryable to a datagrid. I have a partial class which contains extra properties which derive their values based on other values brought in from the database.
Sorting works fine on fields that are actually in the database but not for the derived fields. When I attempt to sort on such a field I get an error saying "The member 'Trip.Difference' has no supported translation to SQL. how to allow sorting on these derived fields?
I'm new to linq. here is the scenario i need to write query for.I have a "Candidate" table with a varchar property "Skill"I have the table OR-mapped with LINQ to SQL on dbml file. Now I want to write linq query that:Selects all Candidates that have skill containing any of the keywords from ("asp.net","php","java")
