I am trying to query a Azure Table Storage. For that I use the following two methods:
TableServiceContext:
public IQueryable<T> QueryEntities<T>(string tableName) where T : TableServiceEntity
{
this.ResolveType = (unused) => typeof(T);
return this.CreateQuery<T>(tableName);
}
Code that uses the method above:
CloudStorageAccount account = AzureConnector.GetCloudStorageAccount(AppSettingsVariables.TableStorageConnection);
AzureTableStorageContext context = new AzureTableStorageContext(account.TableEndpoint.ToString(), account.Credentials);
// Checks if the setting already exists in the Azure table storage. Returns null if not exists.
var existsQuery = from e in context.QueryEntities<ServiceSettingEntity>(TableName)
where e.ServiceName.Equals(this.ServiceName) && e.SettingName.Equals(settingName)
select e;
ServiceSettingEntity existingSettginEntity = existsQuery.FirstOrDefault();
The LINQ query above generates the following request url:
http://127.0.0.1:10002/devstoreaccount1/PublicSpaceNotificationSettingsTable()?$filter=(ServiceName eq 'PublicSpaceNotification') and (SettingName eq 'expectiss')
The code in the class generates the following MissingMethodException:
I have looked at the supported LINQ Queries for the Table API;
Looked at several working stackoverflow solutions;
Tried IgnoreResourceNotFoundException on the TableServiceContext (usercomments of QueryOperators);
Tried to convert the linq query with ToList() before calling first or default (usercomments of QueryOperators).
but I can't get this to work.
Make sure you have parameterless constructor for the class "ServerSettingEntity". The ‘DTO’ that inherits TableServiceEntity needs a constructor with no parameters.
Related
The documentation for LINQ to SQL translation for Cosmos DB states:
User-Defined Function Extension function: Supports translation from the stub method UserDefinedFunctionProvider.Invoke to the corresponding user-defined function.
However, this function is not publicly accessible in .NET SDK v3 (though it is in v2). So what's the workaround until the bug has been fixed?
There are several workarounds:
Don't use LINQ.
Use LINQ but without calling UDFs, then get the query string using query.ToQueryDefinition.QueryText and manipulate it to insert UDF calls at the places you need them, and then evaluate the SQL string (yuck!).
Hack it. First add a dummy method:
public static object Invoke(string udfName, object[] arguments) { return null; }
Use this method in your lambda expressions whenever you would otherwise use UserDefinedFunctionProvider.Invoke. Implement an ExpressionVisitor that replaces all occurrences of MethodCallExpression mce where mce.Method matches the dummy method by
Expression.Call(null, udfMethod, mce.Arguments[0], mce.Arguments[1])
where udfMethod is
MethodInfo udfMethod = typeof(CosmosClient).Assembly
.GetType("Microsoft.Azure.Cosmos.Linq.UserDefinedFunctionProvider", throwOnError: true)
.GetMethod("Invoke", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static);
Use the resulting expression in your Where, Select etc.
(Add a unit test to check when the bug has been fixed and the hack can be removed.)
I am using the Microsoft.Azure.Cosmos 3.22.1 SDK for my example with the UDF (user defined functions) and it worked fine.
I used the example from microsoft.
It is of course also possible to use the UDF in combination with where clauses.
CosmosClient client = new(endpoint, key);
IQueryable<Product> queryable = client
.GetContainer("database", "products")
.GetItemLinqQueryable<Product>()
.Select(b => new Product{ id = b.id, price = b.price, priceWithTax = CosmosLinq.InvokeUserDefinedFunction("tax", b.price).ToString() });
var productIterator = queryable.ToFeedIterator<Product>();
while (productIterator.HasMoreResults)
{
var responseMessage = await productIterator.ReadNextAsync();
Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(responseMessage));
}
Im building a WebAPI OData solution that handles untyped entity objects, as described in this excellent post. Like that post, I define my EdmModel upfront, and use the MapODataRoute method and pass in the model to use:
config.Routes.MapODataRoute("odata", "odata", ModelBuilder.GetEdmModel());
However, this does not seem to work with ODataQueryOptions parameter in my methods:
Get(ODataQueryOptions query)
{
}
It gives the following error: The given model does not contain the type 'System.Web.Http.OData.IEdmEntityObject'. Parameter name: elementClrType
Is there any way to get ODataQueryOptions to work with MapODataRoute?
You should build the ODataQueryOptions manually in your controller action in untyped mode. Sample code follows,
ODataPath path = Request.GetODataPath();
IEdmType edmType = path.EdmType;
IEdmType elementType = edmType.TypeKind == EdmTypeKind.Collection
? (edmType as IEdmCollectionType).ElementType.Definition
: edmType;
// build the typeless query options using the element type.
ODataQueryContext queryContext = new ODataQueryContext(Request.GetEdmModel(), elementType);
ODataQueryOptions queryOptions = new ODataQueryOptions(queryContext, Request);
Ive managed to do it as follows:
ODataPath path = Request.GetODataPath();
IEdmType edmType = path.EdmType;
private ODataQueryOptions GetODataQueryOptions(IEdmType edmType)
{
IEdmModel model = Models.ModelBuilder.GetEdmModel();
ODataQueryContext queryContext = new ODataQueryContext(model, edmType);
ODataQueryOptions queryOptions = new ODataQueryOptions(queryContext, this.Request);
return queryOptions;
}
This works for most query options, but crashes with $select and $expand: The type 'Collection([Org.Microsoft.Product Nullable=False])' is not an entity type. Only entity types support $select and $expand. Is there a way to avoid this exception gracefully when a client tries to filter with $select and $expand, or should i just write something like
if (Request.RequestUri.Query.Contains("select")) { return errormessage }
Also, and more importantly, how would one apply these query options to an EdmEntityObjectCollection which gets returned in the first method?
queryOptions.ApplyTo(collectionProduct.AsQueryable()); // wont work...
(perhaps it is better practice to dynamically build your collection in regards to the query options anyway)
I am trying to get IEnumerable from linq query below. What am I doing wrong?
IEnumerable<DataRow> results =
context.Database.SqlQuery<DataRow>("SELECT * FROM Customer").AsEnumerable();
DataRow class does not have default (parameterless) constructor, so you can't use it as query parameter type. There is no generic constraints on type parameter, and nothing mentioned on MSDN(!), but column map factory will throw exception if parameter type does not have default constructor:
The result type 'System.Data.DataRow' may not be abstract and must
include a default constructor.
Here is a code which throws this exception:
internal static CollectionColumnMap CreateColumnMapFromReaderAndClrType(
DbDataReader reader, Type type, MetadataWorkspace workspace)
{
BindingFlags flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
ConstructorInfo constructor = type.GetConstructor(flags, (Binder) null, Type.EmptyTypes, (ParameterModifier[]) null);
if (type.IsAbstract || (ConstructorInfo) null == constructor && !type.IsValueType)
throw EntityUtil.InvalidOperation(InvalidTypeForStoreQuery((object) type));
// ...
}
BTW Mapping to DataRow makes no sense, even if it would have default public constructor. Because it is not simple primitive type and it does not have properties which match the names of columns returned from the query (yes, mapping uses properties only).
Correct usage of Linq will be
IEnumerable<Customer> results = context.Customers;
That will generate SELECT * FROM Customer query, and map query results to customer entities. If you really want to use raw SQL:
IEnumerable<Customer> results =
context.Database.SqlQuery<Customer>("SELECT * FROM Customers");
I think we were trying to solve the same problem (Google led me here, anyway). I am executing a raw SQL command through SqlQuery<TElement>(string sql, params object[] parameters and wanted to assert individual properties of the results returned from the query in a unit test.
I called the method:
var result = (db.SqlQuery<Customer>("select * from customers").First();
and verified the data it returned:
Assert.AreEqual("John", result.FirstName);
I defined a private class Customer inside my test class (unfortunately, I'm not using Entity Framework):
private class Customer
{
public string FirstName { get; set; }
}
The properties of Customer must match the column names returned in the SQL query, and they must be properties (not just variables of the Customer class. You don't have to create properties for all of the columns returned from the query.
I am working with code first approach in EDM and facing an error for which I can't the solution.Pls help me
LINQ to Entities does not recognize the method 'Boolean
CheckMeetingSettings(Int64, Int64)' method, and this method cannot be
translated into a store expression.
My code is following(this is the query which I have written
from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
}
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
Please help me out of this.
EF can not convert custom code to SQL. Try iterating the result set and assigning the property outside the LINQ query.
var people = (from per in obj.tempPersonConferenceDbSet
where per.Conference.Id == 2
order by /**/
select new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
}).Skip(/*records count to skip*/)
.Take(/*records count to retrieve*/)
.ToList();
people.ForEach(p => p.CanSendMeetingRequest = CheckMeetingSettings(6327, p.Id));
With Entity Framework, you cannot mix code that runs on the database server with code that runs inside the application. The only way you could write a query like this, is if you defined a function inside SQL Server to implement the code that you've written.
More information on how to expose that function to LINQ to Entities can be found here.
Alternatively, you would have to call CheckMeetingSettings outside the initial query, as Eranga demonstrated.
Try:
var personDetails = obj.tempPersonConferenceDbSet.Where(p=>p.ConferenceId == 2).AsEnumerable().Select(p=> new PersonDetials
{
Id = per.Person.Id,
JobTitle = per.Person.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327,per.Person.Id)
});
public bool CheckMeetingSettings(int,int)
{
///code I have written.
}
You must use AsEnumerable() so you can preform CheckMeetingSettings.
Linq to Entities can't translate your custom code into a SQL query.
You might consider first selecting only the database columns, then add a .ToList() to force the query to resolve. After you have those results you van do another select where you add the information from your CheckMeetingSettings method.
I'm more comfortable with the fluid syntax so I've used that in the following example.
var query = obj.tempPersonConferenceDbSet
.Where(per => per.Conference.Id == 2).Select(per => new { Id = per.Person.Id, JobTitle = per.Person.JobTitle })
.ToList()
.Select(per => new PersonDetails { Id = per.Id,
JobTitle = per.JobTitle,
CanSendMeetingRequest = CheckMeetingSettings(6327, per.Person.Id) })
If your CheckMeetingSettings method also accesses the database you might want to consider not using a seperate method to prevent a SELECT N+1 scenario and try to express the logic as part of the query in terms that the database can understand.
I have an entity that I'd like to compare with a subset and determine to select all except the subset.
So, my query looks like this:
Products.Except(ProductsToRemove(), new ProductComparer())
The ProductsToRemove() method returns a List<Product> after it performs a few tasks. So in it's simplest form it's the above.
The ProductComparer() class looks like this:
public class ProductComparer : IEqualityComparer<Product>
{
public bool Equals(Product a, Product b)
{
if (ReferenceEquals(a, b)) return true;
if (ReferenceEquals(a, null) || ReferenceEquals(b, null))
return false;
return a.Id == b.Id;
}
public int GetHashCode(Product product)
{
if (ReferenceEquals(product, null)) return 0;
var hashProductId = product.Id.GetHashCode();
return hashProductId;
}
}
However, I continually receive the following exception:
LINQ to Entities does not recognize
the method
'System.Linq.IQueryable1[UnitedOne.Data.Sql.Product]
Except[Product](System.Linq.IQueryable1[UnitedOne.Data.Sql.Product],
System.Collections.Generic.IEnumerable1[UnitedOne.Data.Sql.Product],
System.Collections.Generic.IEqualityComparer1[UnitedOne.Data.Sql.Product])'
method, and this method cannot be
translated into a store expression.
Linq to Entities isn't actually executing your query, it is interpreting your code, converting it to TSQL, then executing that on the server.
Under the covers, it is coded with the knowledge of how operators and common functions operate and how those relate to TSQL. The problem is that the developers of L2E have no idea how exactly you are implementing IEqualityComparer. Therefore they cannot figure out that when you say Class A == Class B you mean (for example) "Where Person.FirstName == FirstName AND Person.LastName == LastName".
So, when the L2E interpreter hits a method it doesn't recognize, it throws this exception.
There are two ways you can work around this. First, develop a Where() that satisfies your equality requirements but that doesn't rely on any custom method. In other words, test for equality of properties of the instance rather than an Equals method defined on the class.
Second, you can trigger the execution of the query and then do your comparisons in memory. For instance:
var notThisItem = new Item{Id = "HurrDurr"};
var items = Db.Items.ToArray(); // Sql query executed here
var except = items.Except(notThisItem); // performed in memory
Obviously this will bring much more data across the wire and be more memory intensive. The first option is usually the best.
You're trying to convert the Except call with your custom IEqualityComparer into Entity SQL.
Obviously, your class cannot be converted into SQL.
You need to write Products.AsEnumerable().Except(ProductsToRemove(), new ProductComparer()) to force it to execute on the client. Note that this will download all of the products from the server.
By the way, your ProductComparer class should be a singleton, like this:
public class ProductComparer : IEqualityComparer<Product> {
private ProductComparer() { }
public static ProductComparer Instance = new ProductComparer();
...
}
The IEqualityComparer<T> can only be executed locally, it can't be translated to a SQL command, hence the error