Use Linq-to-sql To Iterate Db Records?
Apr 14, 2010
I asked on SO a few days ago what was the simplest quickest way to build a wrapper around a recently completed database. I took the advice and used sqlmetal to build linq classes around my database design.
Now I am having two problems. One, I don't know LINQ. And, two, I have been shocked to realize how hard it is to learn. I have a book on LINQ (Linq In Action by Manning) and it has helped some but at the end of the day it is going to take me a couple of weeks to get traction and I need to make some progress on my project today.
Click HERE To see my simple database schema. Click HERE to see the vb class that was generated for the schema.
My needs are simple. I have a console app. The main table is the SupplyModel table. Most of the other tables are child tables of the SupplyModel table.
I want to iterate through each of Supply Model records. I want to grab the data for a supply model and then DoStuff with the data. And I also need to iterate through the child records, for each supply model, for example the NumberedInventories and DoStuff with that as well.
For the record I have already written the following code...
Dim _dataContext As DataContext = New DataContext(ConnectionStrings("SupplyModelDB").ConnectionString)
Dim SMs As Table(Of Data.SupplyModels) = _dataContext.GetTable(Of Data.SupplyModels)()
Dim query = From sm In SMs Where sm.SupplyModelID = 1 Select sm
This code is working...I have a query object and I can use ObjectDumper to enumerate and dump the data...but I still can't figure it out...because ObjectDumper uses reflection and other language constructs I don't get. It DOES enumerate both the parent and child data just like I want (when level=2).
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Jun 29, 2009
Private Function GetWebDataGridOKButtonId() As String
Dim ctls As ControlCollection = _
WebDataGrid1.Controls(0).Controls(0).Controls
[Code]....
This is not working for me. I am trying to iterate a control collection and return one control ID.
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Dec 7, 2010
I have a VB .Net linq query that I want to return values from two tables. I currently have this:
Dim query = (From c In db.Client _
Join u In db.Users _
On u.UserID Equals c.UserID _
Where (c.ClientID = 1)
Select c, u).ToList
query (System.Collections.Generic.List(Of )) returns several rows as expected each item containing a c and a u.
How do I iterate through the queries collection?
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Mar 17, 2010
Every LINQ example I have seen for VB.NET anonymous types claims I can do something like this:
[code]...
Now when I go to iterate through the collection(see example below), I get an error that says "Name "x" is not declared. For Each x in Infos It's like VB.NET doesn't understand that Infos is a collection of anonymous types created by LINQ and wants me to declare "x" as some type. (Wouldn't this defeat the purpose of an anonymous type?) I have added the references to System.Data.Linq and System.Data.DataSetExtensions to my project. Here is what I am importing with the class:
[code]...
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Mar 12, 2009
Processing an XML file with LINQ to add records into a table in a SQL Server database via a data context. As we are adding records we need to assign the parents in various other tables. Most of the time we can find the existing parent and use it but sometimes we will need to create a new parent.Thought we could do this like this:
Dim defaultPub As publication
defaultPub = New publication With {.name = e..Value}
Dim pub = _Data.publications.Where(Function(s) s.name =
[code].....
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Jan 4, 2012
How can I use Linq to SQL in Vb.net to combine the records of two tables into a datagrid such as shown in this example:Assume i have two tables tbl1 and tbl2
tbl1:
col1 col2
A1 B1
A2 B2
tbl2:
[Code]...
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Apr 20, 2011
way to write the LINQ query. The parent class is simply a student's name and a list of test score data. The child class is a single test score datum. I want to find the worst (or best) score out of all of the TestScore values and then identify the student who had the best score.
Dim query = From s In studentList _
Where s.ScoreList.Select(Function(d) d.TestScore).Min _
= studentList.SelectMany(Function(g) g.ScoreList).Select(Function(h)
[Code].....
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Jun 1, 2012
Have seen some solutions for C# but do not know how to solve the issue in VB.NET.
Query:
Dim Query = (From t In myEntities.Bookings
Where(t.Ref = Someid)
Select t.People).Sum()
t.Ref field is an Int and so is t.People.
The SomeId value is the primary key of the related table. This issue is that there will not always be records in the Bookings table with a Ref value of Someid - so the query throws the following error.
I have seen others have got around this problem with catching the error, but from reading up on this and as per the error information it seems there should be a solution (in VB.NET) to cast the query or some of the fields in the query to nullable types?
Error is as follows:
The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.
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Jan 25, 2012
I've got a table that caches calculated values for certain dates. I want to use LINQ to select all rows where the calculated value fields are null.But when I use isNothing I get an error that LINQ can't translate this into T-SQL. Is there a way to select null values with link, like this...?
Dim var = From rec As Record In myDataContext.Records Where IsNothing(rec.calculatedValue) Select rec
Other posts on stackoverflow mostly discuss how to avoid or check for null values with LINQ.
Note: I can't just set cacluatedValue's default to -1 to flag records whose calculated value has not been set (and then select those records) because I run queries that sum/average the calculated values. Selecting nulls seems cleaner and less bug-prone.
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Sep 4, 2011
There is one-to-n relationship (foreign-key relationship) between tables As and Bs. Every time a new record is added in As, a trigger "after update" in table As creates n records in table Bs. There are two Linq-to-SQL classes A and B representing the tables As and Bs respectively.The class A contains Bs property an EntitySet(of B). Similarly in class B, there is a property A, an EntityRef(of A)
[Code]...
When above function is executed the result is always 0. Whereas there are six records new records has been added to table Bs every time the above function is executed.
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Oct 14, 2009
I'm using visual basic 2008 express edition by linq to sql for my database operation such as edit records. I did not use any sql server but I'm just using the built-in sql server within the visual basic 2008 express. I tried to revised the codes, no error in syntax but there's an error at runtime and it pops-up a window message saying its error message. What I want is to edit the records which were retrieved from the database into the text-boxes and when you click the button5 whatever the new value on the text-boxes should replace the previous one.The Account field is the field in my Table1 in memrec.dbml which I set up for primary key is true and the rest of the fields are false in its primary key.[code]...
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Oct 19, 2009
Is it possible to do a multiple records editing by linqtosql method in one click event? What I've been trying to do is to edit all the names in the table which are having the same account number. I was able to edit but only one name has been edited and the rest are not.
The codes I used.
Private Sub Button2_Click(------------) Handles Button2.Click
Dim accnt As String
accnt = Textbox1.Text
Dim db As New memrecDataContext()
Dim editrecord = From mem In db.Table1s
[Code] ......
Why is it these codes could only edit records in one datarow?
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Oct 14, 2009
I'm using visual basic 2008 express edition by linq to sql for my database operation such as edit records. I did not use any sql server but I'm just using the built-in sql server within the visual basic 2008 express. I tried to revised the codes, no error in syntax but there's an error at runtime and it pops-up a window message saying its error message. What I want is to edit the records which were retrieved from the database into the text-boxes and when you click the button5 whatever the new value on the text-boxes should replace the previous one.The Account field is the field in my Table1 in memrec.dbml which I set up for primary key is true and the rest of the fields are false in its primary key.The code below still found an error when you run the program and it pops-up a window which says:
NotSupportedException was unhandled - Sql server does not handle comparison of NText, Text, Xml, or Image data types.It highlights a yellow background on the line:
db.SubmitChanges()
These are what I see on each field's property on Table1 in memrec.dbml property window:
Access - Public
Type - String(System.String)
Server Data Type - Text[code]........
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Sep 26, 2009
This is the hardest part of LinqtoSql database handling operations in visual basic 2008 I ever encountered,w/c is the update operation cause Ive been posting this thread several times from the other forum site but noone yet was able to answer my question,examples were given but its not efficient cause it won't specify based on the codes i gave and i know its not easy but im still hoping that one of the answerers of this forum will be able to resolve this particular linqtosql operation codes. I used textboxes in manipulating all data into the database such as displaying records, adding records, & updating records, basically I used with textboxes in doing those database operations. I will give you 3 block of codes w/c corresponds those database operations I used and differentiate from each other inorder for us to determine why one of them has no progress or won't do its operation w/c is the update operation...
*************Block of Codes#1(Adding Records)*************
Private Sub Button1_Click(------------------) Handles Button1.Click
Dim db As New memrecDataContext()
[code]....
I would like you to identify,differentiate, or troubleshoot the block of codes#3, or anyhow, why it has no progress at all or it won't edit and change the records but it runs and no error in regards with its code, and the other 2 blocks of codes were able to successfully do its operations.I was just wandering why only the block of codes#3 is not doing its operation successfully when you change the record being displayed in the textbox.Is there a possible way to edit records in the textboxes?If there is.... Is it possible to debug the block of codes#3 to successsfully do its operation? If you could possibly give an example,can you based it on the block of codes#3?
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May 22, 2011
Basically i have a list(of TransRecord)
vb Public Class TransRecord
Public TableName As String
Public PKs As String
[CODE]...
And want to create a linq filter to select only unique records for TableName + PKs (group by) ... but want it to select only the record with the highest ID for this group by.
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Feb 2, 2011
I'd like to take all suggestion either in C# or VB.NET.I have a DB diagram like the image below. I also include the database script here [URL]In the Students table, CountryId and RoomId column are allowed null. Because some records do not have info about room and country yet.Also, some students do not have essays.I'm doing a joint query with all tables. I want to select all students to project the result like this:Wanted query result.
Here's my current query that gives the result like the image below:
Dim db As New DBDataContext
Dim query = From st In db.Students _
Join c In db.Countries On c.Id Equals st.Id _
Join r In db.Rooms On r.Id Equals st.RoomId _
[code].....
current query result I got only one result back because I have (2) William NoMan record in every table. But I don't get anything about others, like (3) Sync Master who has everything but RoomId.What do I need to modify the query above so it will give me all students like in the wanted query image above?
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Mar 21, 2012
I have users check off lab facilities in a UI. I want to use linq to fetch corresponding records for all of the labs that they have checked off. Basically,
Dim myRecs = (From l As EpiData In myDataContext.EPIDatas Where l.facility= _
one of the checked labs
So basically, I need to write a linq query where the "strings" to match are determined at runtime. Is there any way to do this easily? I know that there is a library out there called dynamic LINQ, but (1) it's in C# and I'm writing in VB (2) I'm really just looking for a single, simple solution for this single case.
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May 17, 2006
I can retrieve records from my Database fine, but I'm having trouble updating records. I am getting a syntax error on [code] I get this error when I change the Last Name (Row 0, Column 1). [code]
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Oct 27, 2009
how to get records into oracle database delete from db & update the records i have successfully connected my vb 2008 win form with oracle 10g.
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Dec 29, 2011
How do I update records in a dataset with records in a transaction file?
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Jan 27, 2012
I'm using a DynamicJsonModelBinder from a blog post to pass my JSON data from JavaScript to my ASP.NET MVC Controller as a DynamicJsonObject.
Have a look at the blog post: [URL]
I converted it for my project to VB.NET : [URL]
Imports System.Dynamic
Imports System.Web.Helpers
Namespace MyNameSpace
[Code]....
This works. In my controller, I can access my jsonObject like this: obj.ID '123
But I haven't got an idea yet how to iterate through all properties. I can get all member names as a IEnumerable String Collection (obj.GetDynamicMemberNames()), but how do I use the TryGetMember method to access the value of a member ?
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Aug 15, 2011
I have a VB Web Application with a bunch of textboxes on it in Default.aspx (Using the basic template in Visual Web Designer 2010 Express). I'd like to iterate through those textboxes using some sort of VB solution if at all possible and clear them when the user presses a button. I've tried using something like this:
Dim cControl As Control
For Each cControl in Me.Controls
If cControl Is TextBox Then
[Code].....
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Jul 7, 2010
[This is a simplified example] I have a collection ("myCollection") in which exists three entries: ("hello", "goodbye", "welcome"). I want to iterate through the collection and if in the collection there is the entry "welcome" I want to take one action, if that entry doesn't exist I want to do something else. Like this (pseudo):
[Code]...
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Jan 15, 2010
I need some help with a LINQ query in VB.Net, please.[code]This works, and returns me the data I need to work with. Now I want to iterate through the groups, using a For Each construct. like this: For Each x In drivers Next...However, the compiler is barking at me, telling me that the "'x' is not accessible in this context because it is 'Friend'."
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May 19, 2011
I have a simple XAML file with a grid in it and textboxes. But when using my code it does not find the textboxes by iteration.
VB.Net:
Dim ctl As FrameworkElement = Me.MainWindow
Code:
Dim ChildrenCount As Integer = VisualTreeHelper.GetChildrenCount(ctl)
'ChildrenCount is always zero
For i As Integer = 0 To ChildrenCount - 1
Dim Child As FrameworkElement = VisualTreeHelper.GetChild(ctl, i)
[Code].....
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Jan 31, 2010
I have a BindingSource bound to a DataTable.
I use the BS Filter and would like to iterate the filtered dataset of the DataTable using the Bindingsource.
I know I can do a MoveFirst and the MoveNext and each time using the BS.Position get the correct row in the underlying DataTable. But how do I know when the sets ends? I'm sure there must be such a property, but what is it?
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Nov 27, 2010
if I run the following code,For each itm in MyList Next if the list is nothing i got an error..Is there a better way to deal with list=nothing than using a condion like [code]
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Apr 26, 2012
I want to iterate through an equation and modify a number e.g. Multiply it by 10, where there is one. How do I do this?
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Mar 26, 2009
I have a structure with types ranging from thread's to control.what im looking for is a easy way to iterate through those item like For eachbut i couldn't get for each to workis there a way to do it
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Dec 15, 2011
I am having trouble looping through the following XML file and returning the proper values at each level.
XML File:
<?xml version="1.0"?>
<Domains>
[code]....
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