I'm using Remote.Linq to serialise / deserialise my Expressions as I want to create the ability to send dynamic expressions from a client application to our web services. Standard .NET expressions cannot be serialised so I'm using Remote.Linq instead.
However, I cannot see how to execute the Expression. Normally I would invoke the Compile() and Invoke() methods to execute the Expression against the data. But Remote.Linq expressions don't support such methods.
The following unit test may explain more clearly what I'm trying to achieve.
[TestMethod]
public void SerializeLinqExpressionsTests()
{
var testdata = GetTestdata();
Expression<Func<ModuleEntityAdmins, ModuleEntityAdmin>> expr1 = m => m.Modules.Find(q => q.Id == 1);
var remoteExpression1 = expr1.ToRemoteLinqExpression();
string strexpr1 = SerialiseExpression(remoteExpression1);
try
{
var deserexpr1 = DeserialiseExpression<Remote.Linq.Expressions.LambdaExpression>(strexpr1.NormalizeJsonString());
//what is the equivalent of doing this with a Remote.Linq Expression?
var compiled1 = expr1.Compile();
var result = compiled1.Invoke(testdata);
Assert.IsNotNull(result);
Assert.IsTrue(result.Id == 1);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
Assert.Fail("Error deserialising LINQ expression tree");
}
}
How do you invoke a Remote.Linq expression?
A remote linq expression may be converted back into a system linq expression and be compiled and executed as such.
However, this is not what you actually want when sending expressions to a server to query data. On server side you want to use the Execute extension methods to execute your expression against a data source. Make sure to add a using for namespace Remote.Linq.Expressions.
Here's the sample code from Remote.Linq source repo:
using Remote.Linq.Expressions;
public interface IQueryService
{
IEnumerable<DynamicObject> ExecuteQuery(Expression queryExpression);
}
public class QueryService : IQueryService, IDisposable
{
// any linq provider e.g. entity framework, nhibernate, ...
private IDataProvider _datastore = new ObjectRelationalMapper();
// you need to be able to retrieve an IQueryable by type
private Func<Type, IQueryable> _queryableProvider = type => _datastore.GetQueryableByType(type);
public IEnumerable<DynamicObject> ExecuteQuery(Expression queryExpression)
{
// `Execute` is an extension method provided by Remote.Linq
// it applies an expression to a data source and returns the result
return queryExpression.Execute(queryableProvider: _queryableProvider);
}
public void Dispose() => _datastore.Dispose();
}
Also, there are additional nuget packages for expression execution with EF and EF Core, so you can simply provide a DbContext to the Execute method.
In addition you may want to check out the demos/samples found in the project's github repo.
Related
I have a Controller that has has a parameter of type Expression<Foo, bool> with the name query however that parameter does not show up in the generated swagger.json file. Instead a lot (>1000) parameters that have names like these show up:
Body.CanReduce
ReturnType.IsGenericMethodParameter
Type.IsGenericType
I would like to tell SwaggerGen to have my parameter just shown up as a string. If it is possible using a Filter, that would be my preferred way, but an Attribute would be fine too.
I already tried using an IOperationFilter, but it did not work as operation.Parameters does not even seem to have a paramater with the name query.
private static readonly Type _expressionType = typeof(Expression);
public void Apply(Operation operation, OperationFilterContext context)
{
foreach (var parameter in context.ApiDescription.ActionDescriptor.Parameters)
{
if(_expressionType.IsAssignableFrom(parameter.ParameterType))
{
// The parameter is found ...
var expressionParameter = operation.Parameters.FirstOrDefault(p => p.Name == parameter.Name);
if (expressionParameter != null)
Debugger.Break(); // ... but is not in the operation.Parameters collection although the >1000 mentioned above are.
}
}
}
P.S. to anyone interested: I'm using a custom ModelBinder and System.Linq.Dynamic to parse a query string to an Expression<Foo, bool>
I'm trying to make a call to a database using RequestFactory with Hibernate/JPA, and I want to retrieve a list of entities with embedded entities returned as well. I know that the .with() method works for methods like .find(), but it doesn't seem to work with custom queries.
The current way I'm doing it is as follows:
I used a named query in the entity class for the query. (Primary Entity is Name, embedded entity is a Suffix entity called nameSuffix)
#NamedQueries({ #NamedQuery(name = "Query.name", query = "select * from NameTable") })
Then in the service class, the .list() method, which is what I'd like to call with RequestFactory, is as follows.
public List<Name> list() {
return emp.get().createNamedQuery("Query.name").getResultList();
}
Finally, this is how I make the call in my client side code:
NameRequest context = requestFactory.createNameRequest();
context.list().with("nameSuffix").fire(new Receiver<List<NameProxy>>(){
public void onSuccess(List<NameProxy> response) {
String suff = response.get(0).getNameSuffix().getText();
}
});
In the above code, it says that getNameSuffix() returns null, which would imply that .with("nameSuffix") does not work with the .list() call like it does with the standard .find() method.
Is there a way to build a call that would return a list of entities and their embedded entities using .with(), or do I need to do it another way? If I need to do it another way, has anyone figured out a good way of doing it?
I think you misunderstood what the method with() is thought for, unless you had a method getNameSuffix which returns the NameSuffixentity. This is what the documentation says about it:
When querying the server, RequestFactory does not automatically populate relations in the object graph. To do this, use the with() method on a request and specify the related property name as a String
So, what you have to pass to the method is a list of the name of the child entities you want to retrieve. I hope this example could be helpful:
class A {
String getS(){return "s-a"}
B getB(){return new B();}
}
class B {
String getS(){return "s-b";}
C getC(){return new C();}
}
class C {
String getS(){return "s-c";}
}
context.getA().fire(new Receiver<A>(){
public void onSuccess(A response) {
// return 's-a'
response.getS();
// trhows a NPE
response.getB().getS();
}
});
context.getA().with("b").fire(new Receiver<A>(){
public void onSuccess(A response) {
// return 's-a'
response.getS();
// return 's-b'
response.getB().getS();
// trhows a NPE
response.getB().getC().getS();
}
});
context.getA().with("b.c").fire(new Receiver<A>(){
public void onSuccess(A response) {
// return 's-a'
response.getS();
// return 's-b'
response.getB().getS();
// return 's-c'
response.getB().getC().getS();
}
});
A few weeks ago I decided to switch from using Linq to SQL to use NHibernate instead. (Reasons include: other Java-based projects use Hibernate; target DB not yet decided; multiple DBs may have to be targeted)
Anyway, I wanted to continue using LINQ and saw that NHibernate has LINQ support. I want to have a small nummber of object access methods and be able to pass a LINQ expression which filters the query but it has not worked as expected.
Here is an example based on the PredicateBuilder from http://www.albahari.com/nutshell/predicatebuilder.aspx
public static Expression<Func<Product, bool>> ContainsInDescription(params string[] keys)
{
var predicate = PredicateBuilder.False<Product>();
foreach (string keyword in keys)
{
string temp = keyword.ToLower();
predicate = predicate.Or(p => p.Description.Contains(temp));
}
return predicate;
}
The Predicate.False statment causes the following error message:
Atf.NUnit.Model.TestLinq.TestProductCID():
System.Exception : Could not determine member type from Constant, False, System.Linq.Expressions.ConstantExpression
The p.Description.Contains statement causes this error message:
Atf.NUnit.Model.TestLinq.TestProductCID():
System.Exception : Could not determine member type from Invoke, Invoke(p => p.Description.Contains(value(Atf.Model.Linq.ProductLinq+<>c__DisplayClass2).temp), f), System.Linq.Expressions.InvocationExpression
I get similar errors when using string.Equals and other such methods.
Am I doing something wrong here? Should I use a different approach?
Following line of code gives me an error saying "The underlying connection was closed".
return this.repository.GetQuery<Countries>().Include(g => g.Cities).AsEnumerable().ToList();
But if I remove .Include(g => g.cities) it works fine.
this code is written in one of the operation in my WCF service, and I try to test it using WCF test client. I tried by calling this operation from MVC application also, and the same issue was occurring there too.
Also, i am using generic repository with entity framework
Repository code (only few important extract)
Constructor:
public GenericRepository(DbContext objectContext)
{
if (objectContext == null)
throw new ArgumentNullException("objectContext");
this._dbContext = objectContext;
this._dbContext.Configuration.LazyLoadingEnabled = false;
this._dbContext.Configuration.ProxyCreationEnabled = false;
}
GetQuery method:
public IQueryable<TEntity> GetQuery<TEntity>() where TEntity : class
{
var entityName = GetEntityName<TEntity>();
return ((IObjectContextAdapter)DbContext).ObjectContext.CreateQuery<TEntity>(entityName);
}
Attempt#1
Created following overloads in repository code:
public IQueryable<TEntity> GetQuery<TEntity>(params string[] includes) where TEntity : class
{
var entityName = GetEntityName<TEntity>();
IQueryable<TEntity> query = ((IObjectContextAdapter)DbContext).ObjectContext.CreateQuery<TEntity>(entityName);
foreach(string include in includes)
{
query = query.Include(include);
}
return query;
}
public IQueryable<TEntity> GetQuery<TEntity>(Expression<Func<TEntity, bool>> predicate, params string[] includes) where TEntity : class
{
return GetQuery<TEntity>(includes).Where(predicate);
}
WCF is now trying to execute following line of code:
return this.repository.GetQuery<Countries>("Cities").AsEnumerable().ToList()
But it still gives the same error of "The underlying connection was closed". I tested it in WCF test client. However, when I debug the repository code it shows the navigation object getting included in result, but the issue seems occurring while trying to pass the output to client (WCF test client, or any other client)
After looking at the code you've now posted, I can conclude that, indeed, your DbContext is being closed at the end of the GetQuery method, and is thus failing when you try to use include. What you might want to do to solve it is to have an optional params variable for the GetQuery method that will take in some properties to be included, and just do the include right in the GetQuery method itself.
I need to parse an expressiontree to get a sql where clause.
Aren't there any classes in the .NET FX or any third party library which already have this abilities ?
I mean Linq2SQL, EntityFramework , all of them have to do this, so does anyone know, if there is something that can be reused instead of reinventing the wheel?
MyType.Where(Func<TEntity,bool>((entity)=>entity.Id == 5)))
now i need to get the corresponding string representing a where clause:
where abc.Id = "5"
this is just an simple example. it should also work with logical conjunctions.
I know I can create the expressiontree and parse it on my own, but i think there could be something already existing, which I'm missing
You could create an ExpressionVisitor with the sole purpose of finding and processing the where calls. Making this task very easy to handle.
e.g.,
public class WhereCallVisitor : ExpressionVisitor
{
protected override Expression VisitMethodCall(MethodCallExpression node)
{
var method = node.Method;
if (method.Name == "Where" && method.DeclaringType == typeof(Queryable))
{ // we are in a Queryable.Where() call
ProcessWhereCall(node);
}
return base.VisitMethodCall(node);
}
private void ProcessWhereCall(MethodCallExpression whereCall)
{
// extract the predicate expression
var predicateExpr = ((dynamic)whereCall.Arguments[1]).Operand as LambdaExpression;
// do stuff with predicateExpr
}
// p.s., dynamic used here to simplify the extraction
}
Then to use it:
var query = from row in table
where row.Foo == "Bar"
select row.Baz;
var visitor = new WhereCallVisitor();
visitor.Visit(query.Expression);