Insert An Entity For A Many-to-many Relationship?
Jun 1, 2009
If I a many-to-many relationship between Users and Roles and I have an instance of a User entity and several Role Ids can I insert a relationship between the two types of entities without having any other Role data and without doing a select on the Roles first? Update:
I might not have been clear enough. I don't have an instance of a Role, only the role id. Is it possible to create the relationship between User and Role without filling a Role object from the database first?
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Dec 5, 2011
I have in my database a table (AccessControl) that describes a sort of users "access control list" for the informations contained in the table Customers and other tables.Example: the entity CUSTOMER is marked by the EntityId #1. If a user belongs to the department #6, he can access the records of customer #16 and #31, but he can't for #14, that can viewed by user in department #3:
[code]...
How can I describe this relationship into the DbContext definition using a fluent Code First approach?
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Jan 18, 2011
connection here and declaration of variable
Dim i As Integer
Dim chk As CheckBoxList
chk = CType(Me.FindControl("chkBx1"), CheckBoxList)
For i = 0 To chk.Items.Count - 1
[Code]...
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Mar 7, 2010
I have 3 tables:
CustomerType
CusID
EventType
EventTypeID
[code]....
Then I want it to automatically insert data into CustomerEventType table based on the last EvenTypeID data that's just inserted and the checks of the CusID that is using CheckBoxList1 bounded from CustomerType (Suppose there are 2 IDs. )After I Click on Insert button the data in EventType table and CustomerEventType table should be:
EventType
EventTypeID
1
CustomerEventType
[code]....
The only question that I have is, what should be the code behind the insert button using VB.NET LINQ-to-SQL to get this result?
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Feb 3, 2010
Basically, I am trying to write a LINQ to Objects statement where the relationship is a grandparent, parent, child relationship. (You could also call it a Master Detail relationship.)
Dim coverages As New List(Of Coverage)
Dim coverage As Coverage
For Each rl In oClaimsPolicy.RiskLocations
[code].....
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Mar 30, 2009
I have a simple Entity Framework. For simplicity's sake I will transform the entity names to Northwind Like.I have a IEnumerable Of Customer and Item Objects
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Jun 20, 2010
VB .NET 4 WinForms application. I have a (DevExpress) grid bound to an IEnumerable(Of MyClass). Whenever a new row is added, the ID defaults to zero (0). On trying to SaveChanges, EntityFramework doesn't realise that being an identity field means it should ignore any contents on insert and just insert the other values. I can't specify null / Nothing because it just keeps the ID as zero. I can add and save instances of MyClass manually, but I'm trying to get it to work where the grid handles adding/initialising/etc new entries. As far as I can tell, the problem is not with the grid but with Entity Framework and the generated SQL and entity classes. {"Cannot insert explicit value for identity column in table 'MyClasses' when IDENTITY_INSERT is set to OFF."}
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Aug 29, 2011
How to update the existing Customer object, Insert new Computer object and Add new WorkOrder using entity framework? [code]
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Mar 11, 2010
I have the following code, that in my head should create a new row in a table:
Dim fin As Boolean
Dim db2 As New ChecklistModeldbmlDataContext
For Each a In bServers
If collection("fin" & a.ServerName) = "true, false" Or collection("fin" & a.ServerName) = "true,false" Then
[Code]...
It only ever adds one record in to the table and then errors with Cannot add an entity that already exists.
Now it should enter 4 rows into the table, but I can't work out why the above gives me that error.
I've also tried having the db2.SubmitChanges() outside of the for each and it just inserts the last row.
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Nov 9, 2011
Given a string of categories, I need to split the string and insert each separate item as a new record using EF.The following does not work since string cannot be converted to Tag:
Dim s = "Books, Novels, Magazines"
s.Split(", ").ToList.ForEach(Function(x) _rdsqlconn.Tags.Add(x))
How can i split the string and insert each as a new tag record?
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May 6, 2010
in a new project I thought I would try to integrate the new Entity Model Framework, but am having some issues/problems and would like to know if there is a solution or workaround that will let me insert a record into a table that has an identity property.At first I thougth it might simply recofnize the storedprocs that I have for insert/update/delte actions, and was a bit discapointed when generating the model ignored all my stored procs. So I thought wll heck maybe it just generates a nice insert method for me. Lets see.So I referenced my model and found that for the table (entity) there was an insert action (method) that had been generated, however what i found is that it explicitly added the primarly key field - which was based on an identity property and will not accept an explicit insert value.So I guess 2 questions
1. How do we work with identity properties
2. How can we take advantage of the performance and securtiy advantages that stored procs offer with SQL server?
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Nov 12, 2010
I'm new to EF. I have some code that successfully inserts a record in a table. However, it uses the autogenerated "addto." method which I understand is depreciated. I've seen references to using the "add" method but am having trouble.[code]What is the "correct" way to insert this record (vb please)?
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Apr 6, 2011
I have a GridView that is tied to an EntityDataSource. Most columns are normal bound columns, but two are itemtemplates. When I attempt a delete on one of the rows I receive the following message:
"A property named 'Building1.building_name' was not found on the entity during an insert, update, or delete operation. Check to ensure that properties specified as binding expressions are available to the data source."
I'm not sure how it is possible that this isn't available, since it displays the element just fine when I'm just viewing - it just throws the error when I attempt deleting a row?
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Jul 27, 2011
I am trying to build a survey engine from an existing database design which is like this.
[Code]...
The line Order By Key.RecordOrder throws a null reference exception and I can understand why. Can someone advise on how to resolve this by just modifying this one query? I am fairly new to LINQ and the necessity to write this project
[Code]...
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Jul 22, 2009
I want to update an entity without loading the entity from the database first. I've accomplished this but only by knowing all of the entities properties and then using the "attachto" method. My issues is i don't want my app to need to remember all of the properties. Example:
[Code]....
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Dec 14, 2011
Entity Splitting: one class, two or more tables.Here is how it is done in C#, but I need to get it working in vb.net.One more thing: the class name and table columns do not match, so I have to be able to map that out, too.I have to get this to work this way because the place I'm working at right now is a vb.net only shop and the database schema is fubar, but they have so much (millions) of lines of code done directly against the database in both asp classic, vb.net, AND asp.net webforms that changing the schema right now is not realistically possible.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Post>()
.Map(m =>
[code]....
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Jan 16, 2011
I am trying to jump from ASP Classic to asp.net. I have followed tutorials to get Entity Framework and LINQ to connect to my test database, but I am having difficulties figuring out ExecuteQuery(). I believe the problem is that I need an "entity class" for my database, but I can't figure out how to do it. Here is my simple code:
Dim db as New TestModel.TestEntity
Dim results AS IEnumerable(OF ???) = db.ExecuteQuery(Of ???)("Select * from Table1")
From the microsoft example site, they use an entity class called Customers, but I don't understand what that means.
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Feb 11, 2011
I am trying to create a generic typed class, but am running into a problem. Here is my basic class definition:
public class QueueObject<T> where T : System.ServiceModel.DomainServices.Client.Entity
{
public string LoadingMessage { get; set; }
public System.ServiceModel.DomainServices.Client.EntityQuery<T> Query { get; set; }
}
I am trying to add instances of this class to a queue
private Queue<QueueObject<Entity>> _queue;
this._queue.Enqueue(new QueueObject<MyEntity> {Query = MyContext.GetMyEntitiesQuery(), LoadingMessage = "Loading some stuff"});
This doesn't work. I get an error saying that QueueObject cannont be converted to QueueObject. I don't understand because MyEntity inherits from Entity.
Public Class QueueObject(Of T As System.ServiceModel.DomainServices.Client.Entity)
Public Property LoadingMessage As String
Public Property Query As System.ServiceModel.DomainServices.Client.EntityQuery(Of T)
End Class
[code]....
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May 13, 2010
c# - Are Microsoft Entity Framework and ADO.NET Entity Framework (.edmx) the same?
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May 17, 2012
I use Visual Basic 2008 Database is Mysql Three tables:
[Code]...
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May 15, 2011
I remember we were taught BASIC (Beginner's All Purpose Symbolic Instruction Code) language in school, when we were in 5th grade. It was purely in DOS-Mode and we basically used it for drawing. Then I learnt Visual Basic 6.0 quite a few years basic. I neve found a similarity between them
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Jan 4, 2011
I have two tables which need to be connected using a one-to-one relationship. In SQL Server 2005, how would I add this relationship to the database diagram, do I just leave the relationship blank? Is there any pre requisite queries I have to add? How do I connect these tables in VB? .. the same way I would connect a one-to-many?I need the Student table to be linked to the Class Table where One student can be in only 1 class.
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Jul 21, 2011
My issue involves relationships and cascaded effects between properties, and I'm wondering what best practices are on this.I have a class that contains a list of varying length of numbers. When editing the list, sometimes the user prefer to set a TargetSum, so that the program enforces the list will always add to this sum. I am accomplishing this by programmatically setting the final element in the list such that list sum = TargetSum. For example, if the user chooses to UseTargetSum, then sets TargetSum = 10, then creates a list of length 4, and enters 1, 4, 2 for the first 3 elements, then the final element is programmatically fixed to 3. The user cannot change the final element themselves.
I do this behind the scenes by handling all necessary events, such as a list element value change, list length change, and the UseTargetSum option change. For each event trigger, it recalculates the last element's value.It works but then there was a bug when loading saved data. If a list is loaded by sequentially adding the elements, the handlers modify each entry. Regarding the example, when the first value of 1 is entered, the handlers say "a value was just added, the sum should be 10, there is currently only one element, so it needs to be 10". So the first element gets changed to 10 behind the scenes. When the second element is next added, the handlers say "a value of 4 was just added, but the first element is already 10, so it should be zero." At the end of the load, the final list reads 10,0,0,0 instead of 1,4,2,3.
I know it is possible to rearrange the load procedure such that I get the correct list. For instance, I could avoid enabling the TargetSum event handlers until after all the data is loaded. The list would first be created as 1,4,2,3 and then the handlers would change nothing.
But this experience makes me wonder if I am opening the door for other sneaky side effects. It seems you should be able to load data without worrying too much about an implicit ordering. It also seems unusual to have "cascading" effects between class properties. Is there a more accepted approach?
The other alternative I'm considering is to only enforce TargetSum only inside UI forms. Ie, when you know it's a user making the change, then enforce the TargetSum, but otherwise leave the core class logic alone.That way database loads, etc, are left unaffected. But I guess the downside of not having ubiquitous enforcement is that opens the door of incorrect sums via some unforeseen complication.
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Mar 14, 2011
I have made a small "front-end" application for an Access databasefile.
I set up 3 tables with relations in Access, and added the database as a datasource in my project. I have done no database programming, and the app has worked nicely for about 2 years. It's a simple master-detail form with 2 datagridviews dragged from the datasource window.
Yesterday I opened the project to add a new form. The form is just a "setttings form" with no database activities.
When I press F5 - the main form do not start, and I get the error message "DataMember property '{0}' cannot be found on the DataSource." - where the property name is the name of one of the 2 relationships in the datasource.
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Feb 22, 2009
Im would like to create relationships between my tables from different database. im using VB 2008 and SQL 2008 as my database. Is the relationships should be made on my database itself or tru coding in my VB? If either which how can i do that.
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Dec 15, 2011
How do we create relation ships between tables using a sql query?im using MS Access and VB.net.
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Jul 13, 2009
I cannot figureout to which class ItemStatus should link to!please refer to my blog in the following link to detail description of the issue
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Sep 8, 2009
I'm using a dataset class written by others who have defined the foreign key relationships between tables using the tools in the schema diagram. I'm binding the dataclass to a windows form. I'm running into an issue where I have an existing header record and I'm trying to insert data into a child table via a grid programmatically. The child table contains all keys for data. As the grid is bound to a binding source, I'm simply adding rows directly to the grid programmatically.
When I attempt to save the data, I get the error ForeignKeyConstraint FX_Activity_UserRoleActivity Requires Child Key Values (4) to exist in the parent table. The value (4) is one of the foreign key values and it does exist in the parent table. The error occurs when I tell the bindingsource associated to the child table on the form to EndEdit. Looking at the XSD file for the dataset, both foreign keys are set up for 'Both Foreign and Key Constraint' with Cascade set for both update rule and delete rule. Accept/Reject rule is set to none.
Running a SQL trace, I confirmed that SQL Server is not generating the error, so it is occurring on the client application somewhere. First what does the error actually mean? Second, does the configuration of the foreign key relationship in the dataset's XSD file have anything to do with it? If so how should the foreign keys be set up between the tables? If it isn't how would you go about troubleshooting this issue as stepping through the code ends with the .EndEdit call to the binding source.
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May 8, 2010
StudentId is a foreign key in StudentSubject,What I want know is how do I illustrate the relationship between the two tables is many to one
StudentSubject
StudentID Subject
148 Art
148 History Of Art
145 English
145 Poetry
128 Chemistry
128 Physics
128 Biology
123 Math
StudentLocation
Student RoomNumber
123 1a
145 3b
148 4c
128 2a
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Jun 9, 2011
I am trying to input value to AppSchedNumber into my AppInfo table which is the primary key of my AppExamSchedule (auto inrement). The problem is I can't insert on my AppInfo because my AppSchedNumber on my AppExamSchedule should be the same.
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