.net - Use LINQ To Find MAX Or MIN Of A Field From All Child Records

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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.net - Write A Linq To Sql Query To Find Records Where Field Name Can Match One Of Dynamic Number Of Strings?

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.

Select All Records Where A Field Is Null Using LINQ?

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.

Filter Parent / Child Table In Linq Query Based On Entities In Child Table?

Jul 9, 2010

I have a table (Projects) which is linked to projectVersions on projectID..projectVersions contains several columns on which I'd like to filter a returned project (and associated projectVersions) list. For example there is a "capacity" column and a "country" column. I am doing a filtered list of projects on one page and I'd like to include all projects where any one of the associated projectVersions has a capacity of 750ml and a country of "France" for example.It may be that a particular parameter is not set and so I pass a zero to indicate not to filter on that.I guess this needs some kind of subquery as when I try and do something like this: [code] it doesn't work as the "xxx" bit, being one-to-many, expects me to specify an item to get at the entities within and yet I want to query where ANY of the associated versions match one of the criteria.

Adding Parent And Child Records To MySQL Db?

Oct 28, 2011

I was asked to create a program that inserts records into one parent table and multiple child tables. My question is, how do I know what the PK is for the parent table, so that I may add it as a FK in the child? The PK for the parent is an auto number. As I stated in my title, I'm using VB.net, mySQL, through an ODBC connection. I have to do this through the code and cannot use stored procedures.

my transaction looks like this:

Dim cmdText As String = "INSERT INTO candidate(first_name, last_name, phone1, phone2, email1, city, " _
& " state, country, zip,primary_contact_id ) VALUES (?,?, ?, ?,?,?, ?,?,?,?)"

[Code].....

Child List For Field GridView1 Cannot Be Created

Oct 29, 2009

I have an error in my application, "Child list for field GridView1 cannot be created."[code]./..

Child Tries To Delete A Character From A Previous Field?

May 3, 2010

I am making a small and very simple game that is ment to help children learn to recognise letters. I have come to a stop as I have 3 text fields. When something is entered into the first field, the program will set focus to the next text field. The problem is when the child tries to delete a character from a previous field as the focus is already set to the next text field. I want it to delete the character from the previous field when the backspace bar is hit. Any suggestion how this might be done?

Get Active Child Input Field On Window?

Aug 29, 2010

I am having trouble catching getting the currently active text input on a 3rd party window.

If I use GetForegroundWindow it returns the handle of the main process of that window.

Use LINQ Add CHILD VALUE Always 1?

Jul 19, 2011

Use LINQ add CHILD VALUE always 1?I have the Tables [code]...

[2008] Adding Records To DGV - But Not Updating The PK Field

Feb 7, 2009

I know that when I add a record to a table through a binding source using a binding navigator - it completely handles the IDENTITY PK (it's bound to a textbox and you can see it immediately).

Now I'm trying to do this differently in another part of the program - here I only have a BINDING SOURCE - that's bound to a DATAGRIDVIEW.

I put a new record into the DGV like this

Private Sub vendorfilesDGV_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles vendorfilesDGV.DragDrop
If e.Data.GetDataPresent(DataFormats.FileDrop) Then

[Code]....

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Child List For Field Cannot Be Created Error Message

Jun 15, 2011

im getting error after I run an UPDATE sql query and the datagridview needs to update....not sure what the problem is. heres my code, first block is what the program does on load, the second block is where im getting the problem.

Code:
Private Sub btnUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdate.Click
Module1.Main()

[Code].....

Create The Relationship So That When Move Thruogh Master The Child Have Corresponding Records?

May 21, 2009

I created a dataset.xsd and it contains two table adapters and these table adapters use stored procedure for select.in my vb form, i get value in text box and then fill table using tableadapter and pass parameter to sp. Till this point everything is working fine. Now these tables have relations and i want to create relationship and show the data from child table on basis of master table. How i can do it?

Example

Me.MasterTableAdapter.Fill(Me.dataset1.spMaster, 1) --1 is parameter which is passed to sp
Me. ChildTableAdapter.Fill(Me.dataset1.spChild,1) --same parameter is passed to child table.

Now i have the records in spMaster and spChild. how i create the relationship so that when i move thru Master the child have corresponding records?

LINQ To XML And Child Objects?

Nov 20, 2009

I am creating a tool that interfaces with an API for a CD/DVD burner. I have created several custom classes that will hold the information for the disk sets (which consist of a data path and a label file among other information. The DiskSet class has a list of Include objects. My proposed XML output would be something similar to the following:

<DiskSets>
<DiskSet>
<Name>MySet 1</Name>

[code].....

I am attempting to traverse the Includes collection (I have tried List and Binding List as I am also using this in a pair of datagridview controls) and it keeps returning Expression of type 'Object is not queryable. Make sure you are not missing an assembly reference and/or namespace import for the LINQ provider." How can I use LINQ to pull a list of the Include objects under each DiskSet object for transformation into XML? I am hoping to keep this restricted to this one block of code if possible.

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).

Getting Error Message Child List For Field VwMedicalRecords Cannot Be Created

May 28, 2010

I'm using a stored procedure to fill my dataset. The stored procedure retrieves the data from a view named "vwMedicalRecords". When I bind the result to a windows DataGridView control for the first time the binding work fine but the second time it fails with the above error message.

I placed a refresh button on the form which I use to rebind the datagridview (reloading data).So the first time as I mention its working fine the second time fails third time work fine fourth time fails and so on.

[Code]...

Loop Through Child - Bind Textbox To Field Of Parent Table

Mar 22, 2010

First I have 2 tables, for example Customer and Orders, and in the database there is a foreign key relation between both. For clarity Orders have a foreign key field to the primary key of Customers, thus Customer is the parent and Orders is the child table of the relation. My application is a Windows Form application, and I add a dataset to the project, in which I drop the 2 tables, and the relations between the 2 tables is automatic added. Now I will om a form loop through the Orders table (witch is the Child table) and show in a textbox some fields of the Orders table and also the Name field of the related record of the customers table. Regarding binding a textbox fo a Orders field I do it this way,

Dim myDs As New DataSet1
Dim myAdpCustomer As New DataSet1TableAdapters.CustomerTableAdapter
Dim myAdpOrders As New DataSet1TableAdapters.OrdersTableAdapter
myAdpCustomer.Fill(myDs.Customers)
myAdpOrders.Fill(myDs.Orders)
Dim myBindingSource As New BindingSource
myBindingSource.DataSource = myDs.Orders
myBindingNavigator.BindingSource = myBindingSource
TextBox1.DataBindings.Add("Text", myBindingSource, myDs.Orders.OrderIDColumn.ColumnName)

But now I can't find how to bind a textbox to a field of the Customers table witch is the Parent table of the relation.

Add Child Elements To Existing Xml - Linq?

Aug 17, 2009

I'm having trouble adding child elements to the below
<securities>
<security id="040104JC6">

[code]....

Xpath - LINQ To XML Sum Child Nodes In .NET?

Nov 1, 2011

I have the following XML from Amazon's Marketplace API. I need to sum all the values of Item/ItemPrice/Component[type='Principal']/Amount for all Items to compute an order total. Is this possible to do using LINQ to XML in VB.NET?

<?xml version="1.0"?>
<AmazonEnvelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="amzn-envelope.xsd">
<Header>
<DocumentVersion>1.01</DocumentVersion>

[code]....

Using A Text Field Or Combo Box In A Form To Filter Records In A Datagrid?

Sep 17, 2009

I have a form that has a combo box and a sub form which displays as a datasheet or aka. datagrid. I would like as i type text into the combo box that the datagrid scroll to the matching record.

Adding Related Records In LINQ?

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].....

Linq To SQL Combine Records Of Two Tables?

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]...

Aggregating Parent/child Tables Using Linq To SQL?

Sep 18, 2009

I'm having a nightmare with LINQ. I've got a table of Projects, and each project has many InvoiceHeaders. The Invoice header had a field AmountNet - the value of the invoice.

I want to retrive, for arguments sake, all of the fields from Projects, with the count of invoice headers and the sum of AmountNet. I.e. list of my projects, how many invoices I've raised and the value.

Doesn't sound hard does it.... well, I've just spent the best part of two hours charging through Google and SO to find a solution.

[Code]...

C# - LINQ - Select All In Parent-child Heirarchy

Mar 12, 2012

I was wondering if there is a neat way do to this, that DOESN'T use any kind of while loop or similar, preferably that would run against Linq to Entities as a single SQL round-trip, and also against Linq To Objects. I have an entity - Forum - that has a parent-child relationship going on. That is, a Forum may (or in the case of the top level, may not) have a ParentForum, and may have many ChildForums. A Forum then contains many Posts.

What I'm after here is a way to get all the Posts from a tree of Forums - i.e. the Forum in question, and all it's children, grandchildren etc. I don't know in advance how many sub-levels the Forum in question may have. (Note - I know this example isn't necessarily a valuble use case, but the Forum object model one is one that is familar to most people, and so serves as a generic and accessible premise rather than my actual domain model.)

Creating Objects From Child Elements Using LINQ To XML

Feb 1, 2011

Is there any way to use a LINQ to XML to query an XML document like the one below to create new (anonymous or strongly typed) objects from the child elements of a descendant? Here is my XML document:

[Code]...

Linq To Entities Query With Child Objects?

Oct 13, 2011

Basically I have the follwing:Dim ctx As New AdminCoreEntities Dim roles = (From r In ctx.Roles where r.Name.StartsWith("cust") Select r) 'list of System .Linq.IQueryable(Of AdminCoreModel.Role)

[code]...

The error i get when i run this is: Unable to cast object of type System.Data.Objects.ObjectQuery`1[AdminCoreModel.Role] to type AdminCoreModel.Role

Basically I have a many to many situation and I try to get all the Quicklinks objects queried by their roles and not quite sure why EF will cast to a single AdminCoreModel.Role when i.Roles is a collections of objects.

Linq To Xml - Persisting MDI Child Position And State?

Sep 22, 2010

In a MDI WinForm I want to save each child window position and state, per application user, that is different by the logged in Windows user. My application has its own users; so I won't use the user settings like my.Settings... etc.One option is to read/write directly to the database, but I don't like the idea to access the database for something so trivial as the windows positions. The plus is that I could store that information independently by the machine where the user works, wherever she logs in, her preferences will be remembered.Another option, that I'd like to follow, is to use Xml to store that information in a file locally on the user's computer. The structure could be something like:

<form name="form name">
<Top>120</Top>
<Left>100</Left>[code]....

how this could be done; maybe using Linq to Xml? I've found I can write something as simple as

Dim formPos As XElement = _
<User><%= My.Application.connectedUser.id %>
<form1>[code].....

2) How to write the XElement when finished building it. Should I use an XmlWriter.Create? Hot to pass it the XElement?

3) What happens when in the Xml file there's already a node with the same name, I want to overwrite the previous user settings if they are already there, but not append to the file, nor rewrite the entire file, of course.

Reading XML Element & Child Nodes Using LINQ

Aug 26, 2009

I am new in LINQ world.I need an urgent help in reading the xml elements using LINQ with specific where condition.I need to find the max air_temp for a county i.e where county name = "Boone" and hour id = "06/03/2009 09:00CDT".[code]

Linq Update A Signle Field?

Jun 19, 2009

I am using database compact and i loaded it on my form and i want to update a single field but I cannot, why:

what am doing is:
dim newrec as datatable=(studentdataset."TableName")
dim querie= from det in newrec.asnumerable() _

[code].....

LINQ To EF Sum Function Error When No Records Returned

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.

Cannot Access Child Value On Newtonsoft.Json.Linq.JProperty

Apr 4, 2012

I am trying to parse the json values from the following stream[code]...

I am trying to get all the children values for that property name source. Now if I use JsonTextReader I can read through everything but this is tedious and prone to errors.

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