.Net Core 3.1 application. ConfigureServices in Startup.cs sets up an EF Core 5 DbContext. One of the "static" tables I wish to load into memory and make available via a AddOptions to make the table injectible throughout the application (cheap man's caching). Same as BINDing from appsettings but using an EF Core database.
I already "seed" the database in Main by creating a scope and getting the DbContext service to run an initialization method. That technique won't work in this case because I am adding a service. Is there a way to read the DbContext while I am still in ConfigureServices? A way to add a service once the Host is built but not run?
How would you approach this?
Wouldn't you know. I post the question and kept reframing my search terms and digging and voila.
Using IConfigureOptions
So I created a class
using MyContexts;
using MyModels;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using System.Linq;
public class LoadMySettings : IConfigureOptions<MySettings>
{
private readonly IServiceScopeFactory _serviceScopeFactory;
public LoadMySettings(IServiceScopeFactory serviceScopeFactory)
{
_serviceScopeFactory = serviceScopeFactory;
}
public void Configure(MySettings options)
{
using (var scope = _serviceScopeFactory.CreateScope())
{
var provider = scope.ServiceProvider;
using (var dbContext = provider.GetRequiredService<MyContext>())
{
options.MySettingsList = dbContext.MySettingsTable.ToList();
}
}
}
}
and embedded this in ConfigureServices:
services.AddSingleton>IConfigureOptions<MySettinmgs>, LoadMySettings>();
I have a very weird problem with Unity here. I have the following:
public class UnityConfig
{
public static void RegisterTypes(IUnityContainer container)
container.RegisterType<IDBContext, MyDbContext>(new PerThreadLifetimeManager());
container.RegisterType<IUserDbContext>(new PerThreadLifetimeManager(), new InjectionFactory(c =>
{
var tenantConnectionString = c.Resolve<ITenantConnectionResolver>().ResolveConnectionString();
return new UserDbContext(tenantConnectionString);
}));
}
}
and then in the WebApiConfig.cs file within the Reigster method:
var container = new UnityContainer();
UnityConfig.RegisterTypes(container);
config.DependencyResolver = new UnityResolver(container);
Basically, what I want to happen in the above code is on every request to the API, I want Unity to new up a UserDbContext based on the user (multi-tenant kind of environment). Now the TenantConnectionResolver is responsible for figuring out the Connection String and then I use that connection string to new up UserDbContext.
Also note (not shown above) that TenantConnectionResolver takes an IDbConext in its constructor because I need it to figure out the connection string based on user information in that database.
But for some reason, the code within the InjectionFactory runs at random times. For example, I call //mysite.com/controller/action/1 repetitively from a browser, the code in the InjectionFactory will occasionally run but not on each request.
Am I incorrectly configuring Unity? Has anybody encountered anything similar to this?
Thanks in advance
The problem is very likely related to the LifetimeManager you are using. PerThreadLifetimeManager is not adapted in a web context, as threads are pooled and will serve multiple requests in sequence.
PerRequestLifetimeManager is probably what you want to use.
I have a web api project that I'm building on an N-Tier system. Without causing too many changes to the overall system, I will not be touching the data server that has access to the database. Instead, I'm using .NET remoting to create a tcp channel that will allow me to send requests to the data server, which will then query the database and send back a response object.
On my application, I would like to use entity framework to create my datacontexts (unit of work), then create a repository pattern that interfaces with those contexts, which will be called by the web api project that I created.
However, I'm having problems with entity framework as it requires me to have a connection with the database. Is there anyway I can create a full entity framework project without any sqlconnections to the database? I just need dbcontexts, which I will be mapping my response objects and I figure that EF would do what I needed (ie help with design, and team collabs, and provide a nice graphical designer); but it throws an error insisting that I need a connection string.
I've been searching high and low for tutorials where a database is not needed, nor any sql connection string (this means no localdb either).
Okay as promised, I have 3 solutions for this. I personally went with #3.
Note: Whenever there is a repository pattern present, and "datacontext" is used, this is interpreted as your UnitOfWork.
Solution 1: Create singletons to represent your datacontext.
http://www.breezejs.com/samples/nodb
I found this idea after going to BreezeJS.com's website and checked out their samples. They have a sample called NoDb, which allows them to create a singleton, which can create an item and a list of items, and a method to populate the datacontext. You create singletons that would lock a space in memory to prevent any kind of thread conflicts. Here is a tid bit of the code:
//generates singleton
public class TodoContext
{
static TodoContext{ }
private TodoContext() { }
public static TodoContext Instance
{
get
{
if (!__instance._initialized)
{
__instance.PopulateWithSampleData();
__instance._initialized = true;
}
return __instance;
}
}
public void PopulateWithSampleData()
{
var newList = new TodoItem { Title = "Before work"};
AddTodoList(newList);
var listId = newList.TodoListId;
var newItem = new TodoItem {
TodoListId = listId, Title = "Make coffee", IsDone = false };
AddTodoItem(newItem);
newItem = new TodoItem {
TodoListId = listId, Title = "Turn heater off", IsDone = false };
AddTodoItem(newItem);
}
//SaveChanges(), SaveTodoList(), AddTodoItem, etc.
{ ... }
private static readonly Object __lock = new Object();
private static readonly TodoContext __instance = new TodoContext();
private bool _initialized;
private readonly List<TodoItem> _todoLists = new List<TodoItem>();
private readonly List<KeyMapping> _keyMappings = new List<KeyMapping>();
}
There's a repository included which directs how to save the context and what needs to be done before the context is saved. It also allows the list of items to be queryable.
Problem I had with this:
I felt like there was higher maintenance when creating new datacontexts. If I have StateContext, CityContext, CountryContext, the overhead of creating them would be too great. I'd have problems trying to wrap my head around relating them to each other as well. Plus I'm not too sure how many people out there who agree with using singletons. I've read articles that we should avoid singletons at all costs. I'm more concerns about anyone who'd be reading this much code.
Solution 2: Override the Seed() for DropCreateDatabaseAlways
http://www.itorian.com/2012/10/entity-frameworks-database-seed-method.html
For this trick, you have to create a class called SampleDatastoreInitializer that inherits from System.Data.Entity.DropCreateDatabaseAlways where T is the datacontext, which has a reference to a collection of your POCO model.
public class State
{
[Key()]
public string Abbr{ get; set; }
public string Name{ get; set; }
}
public class StateContext : DbContext
{
public virtual IDbSet<State> States { get; set; }
}
public class SampleDatastoreInitializer : DropCreateDatabaseAlways<StateContext>
{
protected override void Seed (StateContext context)
{
var states = new List<State>
{
new State { Abbr = "NY", Name = "New York" },
new State { Abbr = "CA", Name = "California" },
new State { Abbr = "AL", Name = "Alabama" },
new State { Abbr = "Tx", Name = "Texas" },
};
states.ForEach(s => context.States.Add(s));
context.SaveChanges();
}
}
This will actually embed the data in a cache, the DropCreateDatabaseAlways means that it will drop the cache and recreate it no matter what. If you use some other means of IDatabaseInitializer, and your model has a unique key, you might get an exception error, where you run it the first time, it works, but run it again and again, it will fail because you're violating the constraints of primary key (since you're adding duplicate rows).
Problem I had with this:
This seems like it should only be used to provide sample data when you're testing the application, not for production level. Plus I'd have to continously create a new initializer for each context, which plays a similar problem noted in solution 1 of maintainability. There is nothing automatic happening here. But if you want a way to inject sample code without hooking up to a database, this is a great solution.
Solution 3: Entity framework with Repository (In-memory persistence)
I got this solution from this website:
http://www.roelvanlisdonk.nl/?p=2827
He first sets up an edmx file, using EF5 and the code generator templates for EF5 dbcontexts you can get from VS extension libraries.
He first uses the edmx to create the contexts and changes the tt templates to bind to the repository class he made, so that the repository will keep track of the datacontext, and provide the options of querying and accessing the data through the repository; in his website though he calls the repository as MemoryPersistenceDbSet.
The templates he modified will be used to create datacontexts that will bind to an interface (IEntity) shared by all. Doing it this way is nice because you are establishing a Dependency Injection, so that you can add any entity you want through the T4 templates, and there'd be no complaints.
Advantage of this solution:
Wrapping up the edmx in repository pattern allows you to leverage the n-tier architecture, so that any changes done to the backend won't affect the front end, and allows you to separate the interface between the front end and backend so there are no coupled dependencies. So maybe later on, I can replace my edmx with petapoco, or massive, or some other ORM, or switch from in-memory persistence to fetching data from a database.
I followed everything exactly as explained. I made one modification though:
In the t4 template for .Context.tt, where DbSetInConstructor is added, I had the code written like this:
public string DbSetInConstructor(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
“this.{1} = new BaseRepository();”,
_typeMapper.GetTypeName(entitySet.ElementType), entitySet);
}
Because in my case I had the entityset = Persons and entityname = Person. So there’d be discrepancy. But this should cover all bases.
Final step:
So whether you picked solution 1, 2, or 3. You have a method to automatically populate your application. In these cases, the stubs are embedded in the code. In my case, what I've done is have my web server (containing my front end app), contact my data server, have the data server query the database. The data server will receive a dataset, serialize it, and pass it back to the web server. The web server will take that dataset, deserialize it, and auto-map to an object collection (list, or enumberable, or objectcollection, etc).
I would post the solutions more fully but there's way too much detail between all 3 of these solutions. Hopefully these solutions would point anyone in the right direction.
Dependency Injection
If anyone wants some information about how to allow DI to api controllers, Peter Provost provides a very useful blog that explains how to do it. He does a very very good job.
http://www.peterprovost.org/blog/2012/06/19/adding-ninject-to-web-api/
few more helpful links of repository wrapping up edmx:
http://blogs.msdn.com/b/wriju/archive/2013/08/23/using-repository-pattern-in-entity-framework.aspx
http://www.codeproject.com/Articles/688929/Repository-Pattern-and-Unit-of
EF CTP 5. I have a single instance where I would like to get the unproxied entity. I can't seem to find a way to do this. I don't want to disable proxy creation all together, just need it for this one query. Can anyone help?
Here is a simple example:
var myEntity = DbContext.Entities.Find(1);
var unproxy = myEntity...?
I believe the only possibility is to create new instance of DbContext and turn proxy creation off just to execute this query. The reason is that DynamicProxy is type created in runtime which derives from your original entity type and adds tracking and lazy loading functionality. You can't strip the proxy away once you created it this way. Try this:
using (var context = new MyDbContext(connectionString))
{
((IObjectContextAdapter)context).ObjectContext.ContextOptions.ProxyCreationEnabled = false;
var myEntity = context.Entities.Find(1);
}
In Asp.Net Core you can use AsNoTracking().
Eg:
var blogs = context.Blogs
.AsNoTracking()
.ToList();
More info you can find here.
Can anyone point me towards a current library that provides basic wrapping of ADO.NET functionality? I'm looking for something along the lines of the old SqlHelper class and am not really interested in using the Data Access Application Block (as it's a bit of overkill for my simple needs). What is everyone using for working with ADO.NET directly these days?
Update:
I should note that I'm already working with an ORM (Nhibernate); I've just run up against a situation that requires raw ADO.NET calls - so no need to suggest using an ORM instead of working with ADO.NET
Dan, this is a class that I have built up over a few years. I use ADO.NET extensivly. It supports simple things like Fill, NonQuery, Scalar, but also getting a schema, transactions, bulk inserts, and more.
DataAdapter (VisualStudio 2010 solution)
Let me know if you need any more help using this (note: I removed some links to other objects to post this for you, so if it's broken, just let me know).
I've written my own little helper library (one .cs file) here:
https://github.com/jhgbrt/yadal/blob/master/Net.Code.ADONet.SingleFile/netstandard/Db.cs
You can find the non-joined version, tests, and readme here:
https://github.com/jhgbrt/yadal
I ended up going with Fluent Ado.net for this; great little library for doing the simple out-of-band ado.net stuff that pops up every now and then.
Hope it helpful:
public static class DbHelper {
public static IDbCommand CreateCommand(this IDbConnection conn, string sql, params object[] args) {
if (!(conn is SqlConnection))
throw new NotSupportedException();
var command = (SqlCommand)conn.CreateCommand();
try {
var paramterNames = new List<string>(args.Length);
for (int i = 0; i < args.Length; i++) {
string name = "#p" + i;
command.Parameters.AddWithValue(name, args[i]);
paramterNames.Add(name);
}
command.CommandText = string.Format(sql, paramterNames.ToArray());
}
catch (Exception) {
if (command != null)
command.Dispose();
throw;
}
return command;
}
}