I'm using EF7 and SQLite in a Windows Form Project with VS2013.
I created a Context Class that inheretes DbContext and create a DbSet for each of these 3 classes that represent my tables.
public DbSet<Server> Servers { get; set; }
I inserted data and I'm able to show it in a DataGridview
Using this code:
myContext context = new myContext();
gridServer.DataSource=context.Servers.ToList();
The data shows in the grid but this approach dont let me sort, delete or add things. So I research and find out that I need to use a DataSource Object:
I added the Object but this is the part that confuses me.
If I choose the Server Class the grid does not show anything except the name of the "fields" of that class. I'm guessing that is because the class has nothing to do with the database.
So I chose myContext Class. This one has the SqliteConnection and also has the "Server" property that I used in the code to retrieve data so I guess this is the correct one. But when I picked this one I dont get the "fields" of the store class. All I got is a server column that is also empty and other columns that I have no idea were they came from.
This screen shows the grid that I fill with the code above in the right and my failed attempt with the SourceData Object in the left.
So I wonder if you could guide me. Since It looks like I'm missing some steps/configuration or something.
Thanks in advice.
Related
I have a legacy database with a particular table -- I will call it ItemTable -- that can have billions of rows of data. To overcome database restrictions, we have decided to split the table into "silos" whenever the number of rows reaches 100,000,000. So, ItemTable will exist, then a procedure will run in the middle of the night to check the number of rows. If numberOfRows is > 100,000,000 then silo1_ItemTable will be created. Any Items added to the database from now on will be added to silo1_ItemTable (until it grows to big, then silo2_ItemTable will exist...)
ItemTable and silo1_ItemTable can be mapped to the same Item entity because the table structures are identical, but I am not sure how to set this mapping up at runtime, or how to specify the table name for my queries. All inserts should be added to the latest siloX_ItemTable, and all Reads should be from a specified siloX_ItemTable.
I have a separate siloTracker table that will give me the table name to insert/read the data from, but I am not sure how I can use this with entity framework...
Thoughts?
You could try to use the Entity Inheritance to get this. So you have a base class which has all the fields mapped to ItemTable and then you have descendant classes that inherit from ItemTable entity and is mapped to the silo tables in the db. Every time you create a new silo you create a new entity mapped to that silo table.
[Table("ItemTable")]
public class Item
{
//All the fields in the table goes here
}
[Table("silo1_ItemTable")]
public class Silo1Item : Item
{
}
[Table("silo2_ItemTable")]
public class Silo2Item : Item
{
}
You can find more information on this here
Other option is to create a view that creates a union of all those table and map your entity to that view.
As mentioned in my comment, to solve this problem I am using the SQLQuery method that is exposed by DBSet. Since all my item tables have the exact same schema, I can use the SQLQuery to define my own query and I can pass in the name of the table to the query. Tested on my system and it is working well.
See this link for an explanation of running raw queries with entity framework:
EF raw query documentation
If anyone has a better way to solve my question, please leave a comment.
[UPDATE]
I agree that stored procedures are also a great option, but for some reason my management is very resistant to make any changes to our database. It is easier for me (and our customers) to put the sql in code and acknowledge the fact that there is raw sql. At least I can hide it from the other layers rather easily.
[/UPDATE]
Possible solution for this problem may be using context initialization with DbCompiledModel param:
var builder = new DbModelBuilder(DbModelBuilderVersion.V6_0);
builder.Configurations.Add(new EntityTypeConfiguration<EntityName>());
builder.Entity<EntityName>().ToTable("TableNameDefinedInRuntime");
var dynamicContext = new MyDbContext(builder.Build(context.Database.Connection).Compile());
For some reason in EF6 it fails on second table request, but mapping inside context looks correct on the moment of execution.
I have an Open JPA entity and it successfully connects a many-to-many relationship. Right now I successfully get the entire table, but I really only want the ID's from that tables. I plan on calling the database later to reconstruct the entities that I need (according to the flow of my program).
I need only the ID's (or one column from that table).
1) Should I try and restrict this in my entity beans, or in the stateless session beans that I will be using to call the entity beans
2) If I try and do this using JPA, how can I specify that I only get back the ID's from the table, instead of the whole table? So far looking online, I don't see a way that you can do this. So I am guessing there is no way to do this.
3) If I simply just manipulate the return values, should I create a separate class that I will be returning to the user that will return only the required id list to the user?
I could be completely wrong here, but from the looks of it, I don't think there is a simple way to do this using JPA and I will have to return a custom object instead of the entity bean to the user (this custom object would only hold the id's as opposed to the whole table as it currently does)
Any thoughts... I don't think this is really relevant, but people are always asking for code, so here you go...
#ManyToMany(fetch=FetchType.EAGER)
#JoinTable(name="QUICK_LAUNCH_DISTLIST",
joinColumns=#JoinColumn(name="QUICK_LAUNCH_ID"),
inverseJoinColumns=#JoinColumn(name="LIST_ID"))
private List<DistributionList> distributionlistList;
Currently how I get the entire collection of records. Remember I only want the id...
try
{
//int daSize = 0;
//System.out.println("Testing 1.2..3...! ");
qlList = emf.createNamedQuery("getQuickLaunch").getResultList();
}
This is how I call the Entity beans. I am thinking this is where I will have to programatically go through and create a custom object similar to the entity bean (but it just has the ID's and not the whole table, and attempt to put the id's in there somewhere.
What are your thoughts?
Thanks
I believe I just figured out the best solution to this problem.
This link would be the answer:
my other stack overflow answer post
But for the sake of those too lazy to click on the link I essentially used the #ElementCollection attribute...
#ElementCollection(fetch=FetchType.EAGER)
#CollectionTable(name="QUICK_LAUNCH_DISTLIST",joinColumns=#JoinColumn(name="QUICK_LAUNCH_ID"))
#Column(name="LIST_ID")
private List<Long> distListIDs;
That did it.
Sounds like you want something like this in your quickLaunch class:
#Transient
public List<Integer> getDistributionListIds () {
List<Integer> distributionListIds = new LinkedList<Integer>();
List<DistributionList> distributionlistList = getDistributionlistList();
if (distributionlistList != null) {
for (DistributionList distributionList : distributionlistList)
distributionListIds.add(distributionList.getId());
}
return distributionListIds;
}
I had to guess a little at the names of your getters/setters and the type of DistributionList's ID. But basically, JPA is already nicely handling all of the relationships for you, so just take the values you want from the related objects.
I've got an application with a working Entity model generated from an existing database. I have to point my application at a new database, with the same schema, except that the table and column names are different.
For example, my current schema has tables named like "Answer". My new schema that I need to point to has the exact same table, except it is named "tblAnswer".
My columns have also changed. Where as a column used to be called "AnswerId", it's now "zAnswerId". Don't ask about the "z" prefix, it's a long story, but it's on every column.
So, what options do I have to point this existing Entity Model (generated from the database) to a new database and adjust the mappings? I've been experimenting with some of the techniques that are used for "Code First" mappings, as outlined in this guide, but haven't had any luck. I simply don't know if this is the right approach, or if there is something that makes more sense.
Suggestions? Thanks in advance.
You can change the database in the web.config file.
Use data annotations to use the different table and column names.
For example:
[Table("tblAnswer")]
class Answer
{
[Column("zAnswerId")]
public int AnswerId { get; set; }
}
I'm looking for advice on a decent pattern for dropdown list selection and persistence of the selection with POCO EF please.
I have a list of IEnumerable<Country> in my view model where Country is a POCO loaded via EF. There is an Address property on the view model that takes the current or user selected value on it's Country property. Within the view I display these via a Html.DropdownListFor() thus:
Html.DropDownListFor(model => model.Address.Country.Id, new SelectList(Model.Countries,"Id","Name",model.Address.Country.Id)
So far so good and it all works on postback with the default ModelBinder providing me with a view model with the Address.Country populated. However Address.Country is of course only populated with the Id field with default model binding.
Trying to send the Address update back to the DB through EF blows up as this is seen as a new object which doesn't have it's full object graph loaded, only the Id set.
Now I can fix this by loading the full Country object from the db into the Address.Country property on postback before saving based on the selected Id. But this seems like a lot of hard work for anything beyond a simple object graph.
The most "elegant" solution I could think of would be a custom model binder for Country but then that would require the Model Binder to know about the repository for retrieving the full EF object which doesn't seem right to me. I'd also have to repeat this for all other Entities used in Dropdown lists.
Hope this makes sense and any feedback on how others are doing this would be appreciated.
If you set Address.Country to an object, EF expects it to be a full object that's part of the current context, but EF does recognize foreign keys: If your Address object has both a CountryID property and a Country property, it should accept Address.CountryID being set as long as Address.Country itself is null.
In your Address class declare country as virtual
public class Address
{
public virtual Country Country;
}
try this and let me know if it works, Virtual supports lazyloading and you don't have to query explicitly
I've used WCF RIA services with Entity Framework to build a simple application which can display and updates data about school courses. This was done by following the Microsoft tutorials. Now I would like to have a chart which shows a count for how many courses are on a key stage.
Example:
Key Stage 3 - 20 courses
Key Stage 4 - 32 courses
Key Stage 5 - 12 courses
Displayed on any form of chart. I have no problem binding data to the chart in XAML. My problem is that I do not know how to correct way of getting the data into that format. The generated CRUD methods are basic.
I have a few thoughts about possible ways, but don't know which is correct, they are:
Create a View in SQL server and map this to a separate Entity in the Entity Data Model. Generating new CRUD methods for this automatically.
Customise the read method in the existing DomainService using .Select() .Distinct() etc. Don't know this syntax very well labda expressions/LINQ??? what is it? Any good quickstarts on it?
Create a new class to store only the data required and create a read method for it. Tried this but didn't know how to make it work without a matching entity in the entity model.
Something I am not aware of.
I'm very new to this and struggling with the concepts so if there are useful blogs or documentation I've missed feel free to point me towards them. But I'm unsure of the terminology to use in my searches at the moment.
One way to is to build a model class. A model is a class that represents the data you wish to display. For example i might have a table with 10 fields but i only need to display 2. Create a model with these two properties and return that from your data layer.
you can use entity framework to pump data into a new class like so
Model Class:
public class Kitteh
{
public string Name { get; set; }
public int Age { get; set; }
}
Entity Query:
public Iqueryable<Kitteh> getKittehz
{
var result = from x in Data.TblCats
select new Kitteh
{
Name = x.Name,
Age = x.Age
}
return result;
}
If you are interested in the best practices approach to building silverlight applications I would suggest you research the MVVM pattern.
http://www.silverlight.net/learn/videos/silverlight-4-videos/mvvm-introduction/
http://www.silverlight.net/learn/tutorials/silverlight-4/using-the-mvvm-pattern-in-silverlight-applications/
I am attempting a similar piece of work.
I will tell you the approach I am going to use and maybe that can help you.
I am going to create a class in the silverlight project to describe the chartItem: It will have 2 string properties : Key and Value.
Then create a collection object...In your case, this could be a class that has one property of type Dictionary<string,string> myCollection... or ObservableCollection<ChartItem> myCollection
The next step is to do a ForEach loop on the data coming back from the server and Add to your Collection.
myCollection.Add(new chartItem{ Key= "Key Stage 3", Value = "20 Courses" });
myCollection.Add(new chartItem{ Key= "Key Stage 4", Value = "60 Courses" });
myCollection.Add(new chartItem{ Key= "Key Stage 5", Value = "10 Courses" });
... more to follow if you are still looking for an answer
There is no easy way to include Views in Entity Framework as it does not allow any table/view to be included without "Key" (PrimaryKey) which will cause more efforts as you will have to map view manually in EDMX and then map keys etc.
Now we have found out an alternative approach,
Create View called ChartItems in your DB
Create LinqToSQL file ViewDB
Drag View ChartItems in ViewDB
Create ChartItem[] GetChartItems method in your RIA Domain Service Class as follow
public ChartItem[] GetChartItems(..parameters...){
ViewDB db = new ViewDB();
return db.ChartItems.Where(...query mapping...).ToArray();
}
RIA Domain Service Class can contain any arbitrary method that you can directly invoke from client with parameters. It is as simple as calling a web service. And you have to return an array because IQueryable may or may not work in some cases, but we prefer Array. You can try IQueryable but it may not work correctly against linq to SQL.