问题
I am using DbProviderFactories in my data layer (based on Entity Framework) and am using SQLite for my database, but I don't have to have a App.Config to have the following code:
<configuration>
<system.data>
<DbProviderFactories>
<remove invariant="System.Data.SQLite"/>
<add name="SQLite Data Provider" invariant="System.Data.SQLite" description=".Net Framework Data Provider for SQLite" type="System.Data.SQLite.SQLiteFactory, System.Data.SQLite" />
</DbProviderFactories>
</system.data>
</configuration>
Instead I would like to have my data layer put that in programmatically. Anyone know a way to do this?
EDIT:
The reason for this is that I am using a IoC container to pick the data layer and some of my data layers don't need the App.Config values, or have them be hard tied to the data layer.
回答1:
The following will probably cause sunspots and overthrow western civilization. It may even cause a debate about Duct Tape Programming (make it stop!), but it works (for now)
try
{
var dataSet = ConfigurationManager.GetSection("system.data") as System.Data.DataSet;
dataSet.Tables[0].Rows.Add("SQLite Data Provider"
, ".Net Framework Data Provider for SQLite"
, "System.Data.SQLite"
, "System.Data.SQLite.SQLiteFactory, System.Data.SQLite");
}
catch (System.Data.ConstraintException) { }
回答2:
JoshRivers above posted a solution for SQLite. This can in fact be used for other adapters as well- I was able to get it working for MySQL using his example. I have wrapped this into something a bit more generic. This should be run once the application starts and is for the .NET connector version 6.6.5.0 (but I imagine it is good for other versions as well.)
string dataProvider = @"MySql.Data.MySqlClient";
string dataProviderDescription = @".Net Framework Data Provider for MySQL";
string dataProviderName = @"MySQL Data Provider";
string dataProviderType = @"MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.6.5.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d";
bool addProvider = true;
var dataSet = ConfigurationManager.GetSection("system.data") as DataSet;
foreach (DataRow row in dataSet.Tables[0].Rows)
{
if ((row["InvariantName"] as string) == dataProvider)
{
// it is already in the config, no need to add.
addProvider = false;
break;
}
}
if (addProvider)
dataSet.Tables[0].Rows.Add(dataProviderName, dataProviderDescription, dataProvider, dataProviderType);
回答3:
LATE ANSWER:
You can always directly get a factory like this:
DbProviderFactory factory = System.Data.SQLite.SQLiteFactory.Instance;
// (note that the rest of the code is still provider-agnostic.)
Or use your IoC container to resolve the DbProviderFactory, e.g.:
container.RegisterInstance<DbProviderFactory>(SQLiteFactory.Instance);
I prefer not to use the DbProviderFactories.GetFactory because of its limitation of requiring a configuration file (or a hack like in @JoshRiver's answer).
All DbProviderFactories.GetFactory does is, it looks up the registered assembly-qualified name of the factory type using the provider name, and then it gets the value of the static Instance property using reflection.
If you don't want to use the configuration, one of the methods above might be more convenient depending on your use case.
回答4:
Update for EF 6.0+
You can add a DbProviderFactory by registering a IDbDependencyResolver and resolving for the type DbProviderFactory. An example of this is below:
static class Program
{
[STAThread]
static void Main()
{
System.Data.Entity.DbConfiguration.Loaded += (_, a) => {
a.AddDependencyResolver(new MyDependencyResolver(), true);
};
Application.Run(new Form1());
}
}
class MyDependencyResolver : System.Data.Entity.Infrastructure.DependencyResolution.IDbDependencyResolver {
public object GetService(Type type, object key) {
// Output the service attempting to be resolved along with it's key
System.Diagnostics.Debug.WriteLine(string.Format("MyDependencyResolver.GetService({0}, {1})", type.Name, key == null ? "" : key.ToString()));
if (type == typeof(System.Data.Common.DbProviderFactory)) {
// Return whatever DbProviderFactory is relevant
return new MyDbProviderFactory();
}else if(type == typeof(System.Data.Entity.Infrastructure.IProviderInvariantName) && key != null && key == "MyDbProviderFactory"){
// Return the Provider's invariant name for the MyDbProviderFactory
return new MyProviderInvariantName();
}
return null;
}
public IEnumerable<object> GetServices(Type type, object key) {
return new object[] { GetService(type, key) }.ToList().Where(o => o != null);
}
}
you may have to resolve for some additional types as well depending upon what type of overriding you're needing to do and how your project is setup. Basically just start with the code above and continue to debug until you've determined all the services you need to resolve for given your specific requirements.
You can read more about EF dependency resolution at the links below:
- http://msdn.microsoft.com/en-us/data/jj680697.aspx
- https://entityframework.codeplex.com/wikipage?title=EF%20Configuration%20and%20Extensibility
- https://entityframework.codeplex.com/wikipage?title=Rebuilding%20EF%20providers%20for%20EF6
Additionally, you can do this configuration by overriding DbConfiguration as described in the first link above.
回答5:
Chosing the DB provider factory programmatically pretty much defeats the purpose. You might as well use the classes specific to SQLite instead of all of those interfaces, no?
回答6:
In .NET Core 2.1 and later you can use DbProviderFactories.RegisterFactory to programmatically register a DbProviderFactory.
回答7:
see the following snippet
public DataProviderManager(string ProviderName)
{
var _Provider = DbProviderFactories.GetFactory(ProviderName);
}
you need to pass the ProviderName that in your case is "System.Data.SQLite".
you don't need to create the app config section. That section is created by SQLite in the machine.config after the SQLite.net provider is installed.
the whole purpose of the appconfig section is to help you get the list of configured .net providers when you call the following command:
public GetProvidersList() { DataTable table= DbProviderFactories.GetFactoryClasses(); }
回答8:
Even Later Answer
Get it using configuration like above. I've found that this seems to require the provider assembly to be somewhere that the running program can find it.
/// <summary>
/// Creates a DbProviderFactory instance without needing configuration file
/// </summary>
/// <param name="lsProviderName">Name of the provider. Like "System.Data.SQLite"</param>
/// <param name="lsClass">Class and assembly information. Like "System.Data.SQLite.SQLiteFactory, System.Data.SQLite"</param>
/// <returns>A specific DbProviderFactory instance, or null if one can't be found</returns>
protected static DbProviderFactory GetDbProviderFactoryFromConfigRow(string lsProviderName, string lsClass)
{
if (string.Empty != lsProviderName && string.Empty != lsClass)
{
DataRow loConfig = null;
DataSet loDataSet = ConfigurationManager.GetSection("system.data") as DataSet;
foreach (DataRow loRow in loDataSet.Tables[0].Rows)
{
if ((loRow["InvariantName"] as string) == lsProviderName)
{
loConfig = loRow;
}
}
if (null == loConfig)
{
loConfig = loDataSet.Tables[0].NewRow();
loConfig["InvariantName"] = lsProviderName;
loConfig["Description"] = "Dynamically added";
loConfig["Name"] = lsProviderName + "Name";
loConfig["AssemblyQualifiedName"] = lsClass;
loDataSet.Tables[0].Rows.Add(loConfig);
}
try
{
DbProviderFactory loDbProviderFactoryByRow = DbProviderFactories.GetFactory(loConfig);
return loDbProviderFactoryByRow;
}
catch (Exception loE)
{
//// Handled exception if needed, otherwise, null is returned and another method can be tried.
}
}
Another method that gets the Instance field directly from the assembly. It works even when the DLL is somewhere else on the system.
/// <summary>
/// Creates a DbProviderFactory instance without needing configuration file
/// </summary>
/// <param name="lsClass">Class and assembly information. Like "System.Data.SQLite.SQLiteFactory, System.Data.SQLite"</param>
/// <param name="lsAssemblyFile">Full path to the assembly DLL. Like "c:\references\System.Data.SQLite.dll"</param>
/// <returns>A specific DbProviderFactory instance, or null if one can't be found</returns>
protected static DbProviderFactory GetDbProviderFactoryFromAssembly(string lsClass, string lsAssemblyFile)
{
if (lsAssemblyFile != string.Empty && lsClass != string.Empty)
{
Assembly loAssembly = System.Reflection.Assembly.LoadFrom(lsAssemblyFile);
if (null != loAssembly)
{
string[] laAssembly = lsClass.Split(new char[] { ',' });
Type loType = loAssembly.GetType(laAssembly[0].Trim());
FieldInfo loInfo = loType.GetField("Instance");
if (null != loInfo)
{
object loInstance = loInfo.GetValue(null);
if (null != loInstance)
{
if (loInstance is System.Data.Common.DbProviderFactory)
{
return loInstance as DbProviderFactory;
}
}
}
}
}
return null;
}
来源：https://stackoverflow.com/questions/1117683/add-a-dbproviderfactory-without-an-app-config