OK, I've seen a lot of posts on creating generic LINQ statements, but these are usually based on select queries. What I need is a LINQ UPDATE statement that takes a generic parameter for the table to update and a generic parameter for the column to update.
The data model I'm working with has dozens of tables, and each table has potentially dozens of columns. What I'm really driving toward is a single Update statement that allows me to tell it at runtime which table and which column to update.
Dealing with data typing of these dynamically supplied fields will also be an issue since obviously I can't update a DateTime column with a decimal value for example.
So, can anyone point me at some code that shows a LINQ update process using generic parameters for table and column names.
Any help would be greatly appreciated!
You didn't specify Entity Framework with DbContext but if that is what you are using, this is pretty easy. The following code is written to work within the NerdDinner sample which can be downloaded from http://nerddinner.codeplex.com/
This code locates a dinner based on the id and sets the address property to "New Value"
Dinner dinner = db.Set<Dinner>().Find(id);
var entry = db.Entry(dinner);
entry.Property("Address").CurrentValue = "New Value";
db.SaveChanges();
Related
I have an application with a dataset linked to an sql server database. I have updated some of the names or foreign keys and primary keys in the sql server. How do I make those changes translate to the data set. For example, I had a primary key called fk_temsempl_xxxxx. I changed it to fk_temsempl on the sql database. How do I get that change to show in the dataset designer in visual studio?
I have tried running custom tool by right clicking on the dataset and clicking run custom tool. That didnt work. I tried configuring the table adapter of one of the tables where a change occured, but the name of the relation didnt change.
You actually just right click the relation and choose Edit Relation... or double click on the line (when the mouse cursor changes from arrow to drag symbol) but I honestly wouldn't bother; you'll then have further refactoring to do in the code anywhere the relation is used, and it can be heavily used by visual designers.
You also get the problem that VS may not help you with the refactoring: in data binding scenarios most things that can be a source of data can also be a collection of multiple things that can be a valid DataSource. They then rely on a string DataMember to determine which of the collections of data in the data source should be used for the data.
For example, when a bindingsource is bound to list a DataTable, the bindingsource.DataSource property might be the DataSet object that contains the DataTable, and thebindingsource.DataMemberis a string of "YOUR_TABLE_NAME". the BindingSource might not be bound asmyBindignSource.DataSource = myDataSet.MyDataTable`. Refactoring inside strings involves a find and replace
DataRelations in a DataSet are created from foreign keys as they were discovered when the relevant table(s) were added to the dataset but it is important to note that, like DataTables and everything else, they are NOTHING to do with the database schema objects at all - they aren't permanently associated with them, the dataset entities are just set up looking something like the database objects when they (dataset entities) are first created. DataTables are created from only those columns selected, and whatever .NET datatypes closely resemble the types output by the query. For a table of:
Person
------
Name VARCHAR(50)
SSN INTEGER
Birthdate DATE
If you created the table with SELECT * FROM Person you'd get a datatable with Name (string), SSN (int), Birthdate (datetime) but if you made a new datatable in the dataset based on SELECT LEFT(Name, 1) as Initial, PADLEFT(SSN, 20) as PadSSN, DATEDIFF(day, Birthdate, NOW()) as AgeDays FROM Person then you'd get a datatable of Initial (string), PadSSN (string), AgeDays (int) - i.e. the datatable looks nothing like the db table. This concept of disconnection between dataset and db is pervasive, and really the only things that relate in any way to the database are the properties that specify which DB table/column a particular DataTable/DataColumn relates to for purposes of loading/saving data. Your Person.Name datacolumn can be renamed to Blahblah, but it will still have a .SourceColumn property that is set to "Name" - that's how the mapping between dataset and db works; dataset is predominantly completely independent of the db. Renaming a DB column would require a change to the SourceColumn property only
DataRelations don't even have this notion of linking to the parent relation in the database; there's no SourceRelation or SourceFK proeprty because there is no need to. They're set up with the same rules and a generated name all based on the rules of the FK, but then they function independently and only within the dataset. If you rename or even remove an FK from the db the dataset will carry on working in the same restricted way it always did; adding a datarow to a child table when no aprent row exists for it will throw an exception - none of it anything to do with the FK in the db, and the DataRelation can have different rules to the FK (e.g it can cascade deletes when the FK is NOACTION) or even different columns. You can have more or fewer DataRelations than the DB has FKs
Run Custom Tool is not a "contact the DB and see what changes have occurred there and replicate them into the dataset", it is a "turn the XSD that describes the dataset into a bunch of C# classes that implement strongly typed dataset/table/relation/column etc objects". Any time you change the XSD by making an edit in the visual designer and hit save, the custom tool is run. If you edit the XSD directly in a text editor you may need to run it manually to have your changes reflected in c# classes
Reconfiguring a tableadapter probably won't do anything to the relations either; its solely concerned with changing the datatable and tableadapter. If you really want to refresh the relations, delete the datatable from the set and recreate it. Be prepared for a potentially significant mop up/refactoring of code
Ok, so I have 2 entities: Course and Industry
The industry entity is just a reference table which lists all available Industries that can be tagged to a course, to categorizing them. I put in a many to zero or one relationship (a course can choose to have an industry or not, while an industry can be tagged with many courses).
I know I've played around with the diagrams a bit, adding and removing associations in the past.
Now here is the odd part: The column mappings for Course has 2 similar columns, IndustryId and Industry_Id
I suspect it's from a past association, but thought EF would have taken care of that.
Here is the problem:
In my view that creates the course, the IndustryId is the property which needs to be populated. When I create new courses, I see the IndustryId in the database populated.
However, when I access Industry's properties through Course (Course.Industry.Description) nothing is populated. It can't seem to get the Industry entity.
I see the IndustryId populated in the db, so I tried to populate the Industry_Id column. That fixed it.
Weird enough, the property declared in the model is IndustryId, so that column is populated in the db. But when I try to get Industry entities through Course, it needs the Industry_Id, which I don't quite know where it is from.
Anyone have any ideas?
It sounds like in your updating from the database, you changed the column name on your tables from Industry_Id to IndustryId. The next time you updated from the database, EF5 (which can't determine that this is the same column, as it matches on names) dropped the mapping for Industry_Id, and added a new column called IndustryId.
However, you had already created the foreign-key mapping in your EDMX file based on the Industry_Id column - which is why you get the issue around needing it when loading related records.
In general, when using Database-First, whenever you rename a column in the database, you need to update your EF5 model and update / correct any such discrepancies.
In a data model like this (http://alanstorm.com/2009/img/magento-book/eav.png) I want to get the value from an EAV_Attribute using Linq to SQL.
Assuming that an EAV_Attribute only exists in one inherited table (varchar, decimal, int, etc.) how can I get it in a linq query?
I know that I can use the Inheritance for this, but I want to execute it in the SQL Database side...
Is it possible to do a kind of Coalesce in Linq, considering that the elements have different types?
EAV and linq is not a happy marriage. I think your best shot is to create an unmapped property in eav_attribute that resolves the value (as object) from it's typed attribute child. With entity framework, you won't be able to use this property in an expression (i.e. not in a Where or Select), You must convert to IEnumerable first to access it. (Linq-to-sql may allow it because it can switch to linq-to-objects below the hood).
Another option is to create a calculated column of type sql_variant that does the same, but now in t-sql code. But... EF does not suport sql_variant. You've got to use some trickery to read it.
That's the reading part.
For setting/modifying/deleting values I don't see any shortcuts. You just have to handle the objects as any object graph with parents and children. In sql server you can't use cascaded delete because it can only be defined for one foreign key. (This may tackle that, but I never tried).
So, not really good news, I'm afraid. Maybe good to know that in one project I also work with a database that has an inevitable EAV part. We do it with EF too, but it's not without friction.
First of all, I recommend using TPH and not TPT for EAV tables. (One table with multiple nullable value columns (one per type) + discriminator vs. one table per type.)
Either way, if you modelled the value entity as an abstract class (containing the two IDs) with an inheriting entity per value data type that adds the value property, then your LINQ should look like this:
var valueEntity = context.ProductAttributes.Where(pa =>
pa.ProductId == selectedProductId
&& pa.AttributeTypeId == selectedAttributeTypeId)
.SingleOrDefault() as ProductAttributeOfDouble;
if valueEntity != null
return valueEntity.Value;
return null;
Where the entity types are: Product, AttributeType, ProductAttribute, ProductAttributeOfDouble, ... ProductAttributeOfString.
I am running a simple LINQ query that connects to a view and returns all of the data with the id that I send in.
My simple query is:
var data = db.ViewDataAlls.Where(x => x.guidRequirementId == guidRequirementId);
if I run this query in the database:
select * from viewDataAll where guidrequiremendid = '{Guid Id Sent In Here}'
I get 2 rows back, however the LINQ query is returning 2 rows, but the rows are a duplicate of the first row, not 2 unique rows.
Any ideas?
EDIT: if I run this LINQ Query:
List<string> nums = db.ViewDataAlls
.Where(x => x.guidRequirementId == guidRequirementId)
.Select(x=>x.strNumber).ToList();
I get the individual row numbers, but if I just try to pull the entire row I get a duplicate of the first row multiple times...
I had the same problem. I was ready to conclude that this was a bug in Linq-to-SQL. Direct SQL queries against the view worked, Linqpad queries worked, etc... but for some reason querying against a view sometimes (and not even very often mind you, but when I'd find a particular value that failed, it appeared to always do so) failed. I verified that the query being passed by Linq to the SQL Server was correct (from the SQLServer logs), so it appeared the results were being mangled when they were received by Linq. Querying directly against the view or accessing the contents of the view via a defined association gave the same bad results.
Realizing that the problem lay on the receiving side of the query (after the results were passed back to Linq), I finally tracked it down to the way I had added the view to the dbml. Originally I had dragged the view onto the dbml designer surface, and added an association to the table I wanted to link it to, a basic one-to-many association (using an basic fkid == id relationship). However I couldn't access the view from the table in code. I discovered that I needed to add a primary key to the child (view), so I set the id property as the PK. This seemed to work until I got an unexpected exception when doing a .SingleOrDefault() against the view through the association. Knowing that it should be impossible for my data to have more that one hit for the property I was filtering with, I ran it through the debugger, and sure enough I was getting the right number of results (2 in my case), but the second result was just a copy of the first. The same thing the OP saw.
The solution it turns out is to set all the fields of the view as part of the primary key (in the dbml; I only had 3). Somehow, having the id field as the lone PK was not sufficient for Linq. Once I did this I had no further problems. (It may not be necessary to designate every field as part of the PK, so you may wish to experiment, but just the one id is insufficient apparently).
Note that I did have the view set as "not unique" in the dbml, which one would think would keep this from happening. Apparently not so.
Is ViewDataAlls a view or a table. If it's a view, maybe the sql statement generating that view produces duplicates.
Thanks JHurdlow, you save my day. Looks like LINQ does not use the groupby or order-by in the views. In my case, the SQL Statement in the view was correct and data was presented very well, but for any reason when use LINQ on my MVC3 is different and duplicates rows. In my case I had a view with 5 tables and I had to put all fields as PK on the view at ___DataModel.edmx. Now works fine.
This solution implies that all fields must be not-null, otherwise has to use CASE NULL-THEN END on the View schema.
I'm using Linq 2 Sql and I'd like to add a custom member on one of my data type. For example: I have tables Companies, Departments and Employees. Departments has a FK in Companies and Employess has a FK in Deparments. Very simple.
My goal is to add an EmployeeCount property on Company that will, of course, returns the number of employee in the company (by suming the number of employee in company's departments).
As you may know, it's really trivial to do: just add a member on the partial class and do the stuff. The problem is, I now want to sort on this custom member.
How can I write this custom member for Linq to be able to translate the logic into a valid SQL orderby? I tried with a SPROC but did not success.
Any help appreciated!
Fabian
I guess your may need to add this column to your schema, in order for SQL server to recognize it and take in under consideration in his optimizations.
I would have add a trigger that will update this column automaticly upon changes on your data.