ADO.NET :: Can Get A Value Or Null From An Entity Query
Mar 28, 2011
Dim p = From i In context.persons
Order By i.fileNum
Select i.ID, i.fileNum, i.firstName, i.lastName, i.state, i.prPenPals.FirstOrDefault.startProfile, i.prPenPals.FirstOrDefault.endProfile
where for every person, prPenPal can have exactly one or zero records? I can do the above, but when I try to use p as the datasource of a ListView I get The cast to value type 'DateTime' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.
I tried using
but that didn't work. I got a blue squiggly line "Range variable name cannot match the name of a member of the 'Object' class" error I want the date if the record exists, and Null or Nothing if it dosen't.
Dim MediaQuery = From m In dB.DOWNLOADS _Where m.ID = id _Select
which returns a record from the database. One of the fields in the record is a FK to another table. I need to read this value to be able to set a dropdown based on the ID but I can't work out how to access it. For a standard record I can just do the following txtTitle.Text = MediaQuery.FirstOrDefault().TITLE
However with the foreign key it doesn't work like that. I've tried drpGroup.SelectedIndex = MediaQuery.FirstOrDefault().DOWNLOAD_GROUPS.ID where DOWNLOAD_GROUPS is the FK field but it returns Object reference not set to an instance of an object. If you're simply wanting to read some values from a single db record in the entitiy framework and one is a foreign key how should I go about getting the value?
I have a web app for our golf club. When I compute handicap index for each golfer, I have to select the most recent scores and then a subset of those scores depending on how many rounds of golf the golfer has played. All the scores are entered into a single SQL Express table called "Rounds". Verbally, this is what I'm trying to do:
1) select the twenty most recent golf scores (sort on date descending, "take(20)") [if less than 20 records, then select all available];
2) for this set of records, select the 10 lowest scores (or smaller number if golfer has less than 20 rounds);
3) compute the average round differential for the subset of records, etc. to calculate handicap index (this step is working ok...)
My current VB code has this LINQ query (which is flawed -- it selects the lowest handicap differential scores of ALL records for the filtered user):
[Code]....
How do I modify this query to accomplish items 1) & 2) above? It seems this should be simple, but my experience with queries is still limited.
I'm working on a portal, and I need to check users conection on the ldap.
And if users are members of a special group then it works.
I've exactly used this link to make it works : http://msdn.microsoft.com/en-us/library/ff649227.aspx (almost work)
My point is : my ldap path seems good, no error anymore, when I log with my username and password.But when I querry it, it returns null, but I'm sure my user is in the group :
// Bind to the native AdsObject to force authentication. Object obj = entry.NativeObject; DirectorySearcher search = new DirectorySearcher(entry); search.Filter = "(SAMAccountName=" + username + ")"; search.PropertiesToLoad.Add("cn"); SearchResult result = search.FindOne(); if(null == result) { return false; }
I'm a normal user, i test with my account. I'm a member of the group that I'm looking for.
here is my code for selectiong some records from db table
string strSql = "select * from mtblNBD where SentTo=@SentTo and InternalStatus Is NULL order by DeadLine desc"; SqlCommand com = new SqlCommand(strSql, con); com.Parameters.Add("@SentTo", SqlDbType.NVarChar, 50).Value = (string)Session["uname"];
here I am using parameters for SenTo field but not for NULL so it is ok... or should I use parameters for this field where value is NULL , if yes then how can I use parameter for this
I'm using the linq to entity command to perform a record update. I want to set one of the fields back to NULL but I'm not sure how do it. I have a query such as
Dim record = From r in db.LISTS where r.ID = refID Select r record.Title = txtTitle.text if txtDetail.text = "" then record.Detail = end if
I have to change the username column in my database to nullable, which means everywhere in my code, I now have to check username.HasValue and change references to username to username.Value. Is there anything I can do to avoid having to change all the references to username to username.Value?
Normally I work in ASP Classic, and am still a bit green on ASP.Net MVC.
I have my model with its fields or entities (might not be the right word hence why not able to find if previously answered, forgive me), and some of these will have null values such as hyperlinks, email address, specific types of phone numbers, etc.
What I want to do is not write certain blocks of HTML within the foreach loop if a field is empty.
In ASP Classic, I would have written an If statement along the lines of:
<% If RS.field <> NULL then %>HTML with <%=RS.field %><% End If %> <% If RS.field2 <> NULL then %>HTML with <%=RS.field2 %><% End If %> ...
However, I don't know how to achieve the same result in ASP.Net MVC.In one of my current usages, a list of sellers returned for a specific set of search results, it runs through a foreach loop and returns the current HTML (in part):
Website: <a class="url" href="<%= seller.ContactWebsite %>" target="_blank" title="Visit the website for <%= seller.Name %>"><%= seller.ContactWebsite %></a><br />
So, if for example I have a field from the model, say seller.ContactWebsite, and this field was NULL, I would not want it to write this as part of the foreach loop.
Hi guys I need to rewrite the sql query below using Linq to entity. Unfortunately I don't have a lot of experience of using Linq.
With TempTableName AS (SELECT [ColumnName], [ColumnName2], [ColumnName3], [ColumnName4], ROW_NUMBER() OVER (order by ColumnName desc) as RowNumber from TableName ) SELECT [ColumnName], [ColumnName2], [ColumnName3], [ColumnName4] FROM TempTableName WHERE ROWNUMBER Between 10 and 100
Users Id Username Email Password UserStatuses Id Name Users_UserStatus Id User (FK - Users: Id) Status (FK - UserStatuses: Id) StatusDate
As you can see, UserStatuses is a reference table with various statuses. Users_UserStatus is a join table between Users and UserStatuses. Using Entity Framework, how can I do a conditional to check if the latest StatusDate is "Pending"? As of now, I have the following:
I then check whether one of the result values is more recent than six months ago using an if..then like so:
If rhcexists.First.SignatureDate > Date.Today.AddMonths(-6) Then End If
However, if there are no results returned this will return an error. Is there a way for me to tell it to act as if the date is older than six months if there is no value at all? e.g., could I in pseudo do something like:
If Exists(rhcexists.First.SignatureDate, Date.Today.AddMonths(-8)) > Date.Today.AddMonths(-6) Then End If
Need to figure out the correct way to do a simple SUM function in Linq, but also manipulate one of the feilds coming back by doing a Substring on it, here is the original SQL query:
I am having a meltdown over something that seems so simple and yet isn't working. Here's my scenario.
I have an object structure of tEvents, which contains properties of an event like a run of concerts. tEvents in turn contains an entity set of tEventOptions, which include properties like EventDate, Cancelled etc. I would like to query a list of tEvents using properties of the tEventOptions, for example filtering by date.
My pageis using a calendar object to show event dates. So I am trying to find if any tEvents in the List coming back from the database match the date of the day element being rendered in my Calendar control like so (in this snip 'data' is List and results from a db query):
[code]....
Except r, my query result var, is always true no matter what data it receives. I have tried the sub query using other properties of tEventOption and get the same 'true' result each time. I know that the data does not reflect this result so I clearly have a problem with the structure of my query, but for the life of me I cannot find a way to resolve it.
I have this query for getting data through Entity Framework, which works today. Thing is, i want to create the query dynamically, i.e build it up in blocks, but i can't figure out how exactly to do it. I believe if i can somehow save one of the values that i retrieve in the beginning i can do it, but now i retrieve it twice (probably a bit slow as well? Unless the compiler fixes it before quering). Makes sense? Here is the LINQ:
Best way to show the SQL trace of a LINQ query to Entity Framework 3.5? I am using ASP.net and EF 3.5.
Dim dbo As Web.Portal.RBMEntities = New Web.Portal.RBMEntities Dim Query = From RoleAllocations In dbo.RoleAllocations Where RoleAllocations.user_id = _ID And RoleAllocations.expire_date > Today Select RoleAllocations
I can't seem to figure out how to write this query properly. I've tried various combinations but nothing's worked yet. Below is the relevant portion of my database model: I need to select the products that match a given Category and Group, and that match a given Year, Make, Model, submodel. This I've done below:
ItemList = From P In gDataContext.Products.Include("Groups").Include("Groups.Category1").Include("LookupYearMakeModels") From G In P.Groups Where G.Category = Cat And G.Grp = Group From Y In P.LookupYearMakeModels Where Y.Year = YMM.Year And Y.Make = YMM.Make And Y.Model = YMM.Model And Y.Submodel = YMM.Submodel Select P
I now also have to select products that match the Category, and Group but are Universal (Product.Univeral = True). I'm currently writing two queries, the one above and the one below. I'm merging the results of the two by simply using ItemList.AddRange(ItemList2) ItemList2 = From P In gDataContext.Products.Include("Groups").Include("Groups.Category1") where P.Universal From G In P.Groups Where G.Category = Cat And G.Grp = Group Select P But I want to combine both queries into one and avoid merging the results. How can I do it?
I am very new to entity, sql, c#, and asp.net so this might be something easily fixed. I am attempting to display all the inactive products stored in my table called products in a datagrid.
var productQuery = from b in solutionContext.Version where b.Product.Name == search && b.Product.ActiveNumber > b.VersionNumber select new Product { Name = b.Product.Name, Description = b.Product.Description, ID = b.ID, LastNumber = b.Product.LastNumber, MiddleNumber = b.Product.MiddleNumber, RSTATE = b.RSTATE, ActiveNumber = b.Product.ActiveNumber, LastModified = b.Product.LastModified, ParentID = b.Product.ParentID, ProductType = b.Product.ProductType }; ProductsGrid.DataSource = productQuery; ProductsGrid.DataBind();
I am getting this error: $exception {"The entity or complex type 'SolutionsModel.Product' cannot be constructed in a LINQ to Entities query."} System.Exception {System.NotSupportedException}
I've been working on building a back end on an access database that allows users to search records using a web search box. I've been able to successfully set up simple search query's but have run into trouble where multiple criteria with "AND" statements (OR statements would return too much to be useful). My problem is this, when all five text boxes are filled out the query returns records no problem, but if even one is left blank i get nothing what so ever. Is there any thing I can do in either SQL or VB to either ignore null values entirely or convert them to wildcard values?
public class Category { public int CategoryId { get; set; } public string Name { get; set; } } public partial class CategoryMap : EntityTypeConfiguration<Category> { public CategoryMap() { this.HasKey(c => c.CategoryId); this.Property(c => c.Name).IsRequired().HasMaxLength(400); } } public class MyObjectContext : DbContext { public MyObjectContext(string connectionStringName) : base(connectionStringName) { } public DbSet<Category> Categories { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Configurations.Add(new CategoryMap()); base.OnModelCreating(modelBuilder); } }
Now when I run the following code I get an exception (GenericArguments[0], 'System.Int32', on 'System.Data.Entity.Internal.Linq.ReplacementDbQueryWrapper`1[TEntity]' violates the constraint of type 'TEntity')
DbDatabase.SetInitializer<MyObjectContext>(new DropCreateDatabaseIfModelChanges<MyObjectContext>()); using (var context = new MyObjectContext("NopSqlConnection")) { var query1 = from c in context.Categories select c.CategoryId; var test1 = query1.ToList(); //works fine var query2 = from c in context.Categories where query1.Contains(c.CategoryId) orderby c.Name descending select c; var test2 = query2.ToList(); //throws the exception }
I am new to this, and I am trying to implement a linq query similar to db.Genres.Include("Albums") command from
mvc music store using my current DB setup. I realize that the tutorial mentions Checlking the "Include foreign key columns in the method" when creating the tables in ADO.NET, but if I am using LINQ to SQL classes, then how can I obtain the same effect. And how do I use db.Genres.Include("Albums") to simplify my life?
