maybe another one stumbled upon this topic and found a nice solution. Using the HATEOAS REST approach with help of Spring HATEOAS project works pretty well for link building to resources. But in the end, to map flattened resources back to an entity object tree, I need to disassemble my link and query the persistence backend. Example given, I have an entity Item, referencing ItemType (Many-to-one). Natural key of item is the composite of ItemType foreign key and Item code itself. The URL I map in ItemController using the link builder is
#RequestMapping("/catalog/items/{itemTypeCode}_{itemCode}")
Now a unique link for an item is e.g. http://www.sample.com/catalog/items/p_abc123
To invert this link I do some very ugly string work:
#Override
public Item fromLink(Link link) {
Assert.notNull(link);
String baseLink = linkTo(ColorTypeController.class).toString() + "/";
String itemTypeAndItemPart = link.getHref().replace(baseLink, "");
int indexOfSplit = itemTypeAndItemPart.indexOf('_');
ItemType itemType = new ItemType();
itemType.setCode(itemTypeAndItemPart.substring(0, indexOfSplit));
Item item = new Item();
item.setItemType(itemType);
item.setCode(itemTypeAndItemPart.substring(indexOfSplit + 1));
return item;
}
And all the time I am wondering, If there isn't a much nicer and more flexible approach (beware of any query string part, that will break the code) to do this inverse mapping. I actually do not want to call another MVC controller from within a controller but it would be nice, to somehow utilize the dispatcher servlet disassembly functions to deconstruct the URL into something more handy to work with. Any helpful hints for me? Thx alot :)
You can use a UriTemplate. Its match method returns a map of variables and their values that have been extracted from the URI. For example:
UriTemplate uriTemplate = new UriTemplate("/catalog/items/{itemTypeCode}_{itemCode}");
Map<String, String> variables = uriTemplate.match("http://www.sample.com/catalog/items/p_abc123");
String itemTypeCode = variables.get("itemTypeCode"); // "p"
String itemCode = variables.get("itemCode"); // "abc123"
Related
I've migrated concepts from a couple of CQRS frameworks I've seen and just started facing some issues.
I have a common EntityDbContext subclass which I use in any consuming project without further extension to suit the domain of the application, rather I provide interfaces, IReadEntities and IWriteEntities which have methods like Query() and Get() which behind the scenes call Set() returning the DbSet() then allowing the standard LINQ expressions to be chained on as for any EF query. I'm facing issues around using Include() on my IQueryables as I'm using LinqKit with AsExpandable() at the end of all my calls. This is what my context Query methods look like
public new IQueryable<TEntity> Query<TEntity>() where TEntity : class, IEntity
{
// AsNoTracking returns entities that are not attached to the DbContext
return QueryUnfiltered<TEntity>().Where(_recordAuthority.Clause<TEntity>());
}
public IQueryable<TEntity> QueryUnfiltered<TEntity>() where TEntity : class, IEntity
{
// AsNoTracking returns entities that are not attached to the DbContext
return Set<TEntity>().AsNoTracking().AsExpandable();
}
A typical query handler looks like this:
public async Task<IEnumerable<GetCustomerView>> Handle(CustomersBy query, CancellationToken cancellationToken)
{
var customers = _db.Query<Customer>();
// Apply filters
if (!string.IsNullOrEmpty(query.FirstName))
customers = customers.Where(x => x.FirstName.Contains(query.FirstName));
if (!string.IsNullOrEmpty(query.LastName))
customers = customers.Where(x => x.LastName.Contains(query.LastName));
// Execute the query and return the results
var view = await customers.Select(x => new GetCustomerView
{
Id = x.Id,
FirstName = x.FirstName,
LastName = x.LastName,
EmailAddress = x.EmailAddress
}).ToListAsync(cancellationToken).ConfigureAwait(false) as IEnumerable<GetCustomerView>;
return view;
}
This scenario works fine if I wanted to pull address details from a related table as I use projection on the database serve given I'm using the Select prior to execution. There are scenarios though where it makes sense to pull an object graph back and specify Include(...) statements but as it stands specifying _db.Query<Customer>().Include(c => c.Address) doesn't hydrate the Address navigation property. I've tried leaving the AsExpandable() off and then the results come back.
The question is, does anyone see a way to allow the Include statements to be provided maybe as a parameter to the method and then I loop through them and tack them on before calling AsExpandable()? I can't quite get my head around how to do it, if it's possible.
Maybe there's another approach?
Interestingly this apparently works fine on a version of this pattern a colleague uses where they are using EF 6. He says they specify Include after the AsExpandable without a problem.
This is known issue with EF Core and LinqKit AsExpandable (and in general with any extension library which uses custom IQueryProvider to perform its query expression tree preprocessing like LinqKit), because EF Core ignores all EF Core specific IQueryable extensions (Include / ThenInclude, AsNoTracking etc.) it the query provider is different (or does not inherit) the EF Core one (EF6 has no such requirements).
With that being said, currently there is no other solution than applying all EF Core specific extensions before calling AsExpandable.
Ok this works. I created an overload:
public IQueryable<TEntity> Query<TEntity, TProperty>(IEnumerable<Expression<Func<TEntity, TProperty>>> includes) where TEntity : class, IEntity
{
var query = Set<TEntity>().AsNoTracking();
foreach (var expression in includes)
{
query = query.Include(expression);
}
return query.AsExpandable();
}
From my handler I create a list of include expressions and pass to the Query:
var includes = new List<Expression<Func<Customer, object>>>
{
c => c.Address
};
var customers = _db.Query(includes);
var result = await customers.ToListAsync(cancellationToken).ConfigureAwait(false);
Execution of the query has the navigation property populated:
Means I'm not 'Fluent'ly chaining them from the client code's perspective, but I don't think it's terrible.
Thoughts?
I have defined odata route using MapODataServiceRoute in my WebApiConfig.
config.Routes.MapODataServiceRoute("CompanyoOdata", "odata", GetImplicitEdm(config));
private static IEdmModel GetImplicitEdm(HttpConfiguration config)
{
ODataModelBuilder builder = new ODataConventionModelBuilder(config, true);
builder.EntitySet<Company>("Company");
builder.EntitySet<Photo>("Photos");
builder.EntitySet<Country>("Country");
return builder.GetEdmModel();
}
The data service works just fine. But I want to achieve few things.
I don't want to expose my metadata or associations because i'm using it internally and will not need metadata. How can I restrict access to these information (i.e restrict access to http://www.sample.com/odata/#metadata or http://www.sample.com/odata/$metadata)
secondly, I want to ignore some properties from getting serialized. I found two ways of doing this.
Using data contracts and marking properties with [DataMember] attribute or [IgnoreDataMember] attribute
Using Ignore method on EntitySet when building the model
I can't use the first method as I'm using Database first approach for entity framework hence can't decorate the entity with attributes. I thought I can achieve this by using MetaDataType, but it seems it only works for DataAnnotations.
I used second method with success, but you can't pass more than one property in the ignore method. Has to do it to individual property that I need to ignore, which is a bit tedious. Is there another way to do this?
any help really appreciated.
If want to hide metadata (/$metadata) or service document (/), can remove the the MetadataRoutingConvention from existing routing conventions, e.g.:
var defaultConventions = ODataRoutingConventions.CreateDefault();
var conventions = defaultConventions.Except(
defaultConventions.OfType<MetadataRoutingConvention>());
var route = config.MapODataServiceRoute(
"odata",
"odata",
model,
pathHandler: new DefaultODataPathHandler(),
routingConventions: conventions);
If only expose a few properties per type, can use ODataModelBuilder instead of ODataConventionModelBuilder. E.g., some example:
ODataModelBuilder builder = new ODataModelBuilder();
EntityTypeConfiguration<Customer> customer = builder.EntitySet<Customer>("Customers").EntityType;
customer.HasKey(c => c.Id);
customer.Property(c => c.Name);
Web services cannot return an anonymous type.
If you are building a LINQ query using classes through a datacontext... you cannot construct instances of those classes in a query.
Why would I want to do this? Say I want to join three "tables" or sets of objects. I have three items with a foreign key to each other. And say the lowest, most detailed of these was represented by a class that had fields from the other two to represent the data from those. In my LINQ query I would want to return a list of the lowest, most detailed class. This is one way I have decided to "join some tables together" and return data from each of them via LINQ to SQL via a WebService. This may be bad practice. I certainly do not like adding the additional properties to the lowest level class.
Consider something like this... (please ignore the naming conventions, they are driven by internal consideration) also for some reason I need to instantiate an anonymous type for the join... I don't know why that is... if I do not do it this way I get an error...
from su in _dataContext.GetTable<StateUpdate>()
join sfs in _dataContext.GetTable<SystemFacetState>()
on new { su.lngSystemFacetState } equals new { lngSystemFacetState = sfs.lngSystemFacetState }
join sf in _dataContext.GetTable<SystemFacet>()
on new { sfs.lngSystemFacet } equals new { lngSystemFacet = sf.lngSystemFacet }
join s in _dataContext.GetTable<System>()
on new { sf.lngSystem } equals new {lngSystem = s.lngSystem}
select new
{
lngStateUpdate = su.lngStateUpdate,
strSystemFacet = sf.strSystemFacet,
strSystemFacetState = sfs.strSystemFacetState,
dtmStateUpdate = su.dtmStateUpdate,
dtmEndTime = su.dtmEndTime,
lngDuration = su.lngDuration,
strSystem = s.strSystem
}
).ToList();
Notice I have to build the anonymous type which is composed of pieces of each type. Then I have to do something like this... (convert it to a known type for transport via the web service)
result = new List<StateUpdate>(from a in qr select(new StateUpdate
{
lngStateUpdate = a.lngStateUpdate,
strSystemFacet = a.strSystemFacet,
strSystemFacetState = a.strSystemFacetState,
dtmStateUpdate = a.dtmStateUpdate,
dtmEndTime = a.dtmEndTime,
lngDuration = a.lngDuration,
strSystem = a.strSystem
}));
It is just awful. And perhaps I have created an awful mess. If I am way way off track here please guide me to the light. I feel I am missing something fundamental here when I am adding all these "unmapped" properties to the StateUpdate class.
I hope someone can see what I am doing here so I can get a better way to do it.
You can create a 'dto' class which just contains the properties you need to return and populate it instead of the anonymous object:
public class Result
{
public string lngStateUpdate
{
get;
set;
}
... // other properties
}
then use it like this:
from su in _dataContext.GetTable<StateUpdate>()
...
select new Result
{
lngStateUpdate = su.lngStateUpdate,
... // other properties
}
Nitpick note - please ditch the Hungarian notation and camel casing for properties :)
I think the answer is to create another object to serve as a DTO. This object would not be mapped to the data context and can contain fields that cross the mapped objects. This solves the problems of repetitive properties in the mapped objects, and allows for instantiation of the DTO class in the query as it is not mapped.
FYI: with respect to the problem with the join- I revisited that and I think I may have had the inner and outer components of the join switched around before.
Being kind of a newb to MVC 4 (or really any of the MVC's for ASP.NET) I cant help but feel theres more to the URL helper than what I'm seeing.
Basically I've read the tutorials on populating the attributes in a controllers methods using a query string in the URL.
I dont liek query strings though and prefer a sectioned "folder" like style.
Without much further adu, this is the sample URL:
http://something.com/DataTypes/Search/searchString
this approach is actually pretty safe as there will only ever be single worded searches
I have tried in the DataTypes controller
[HttpGet]
public ActionResult Search(String q)
{
ViewBag.ProvidedQuery = q;
return View();
}
and a few other small variations, right now im just trying to get the string to show up in the view but I dont seem to be getting anything there.
Is there anyway to inject the 3rd string in the url into an attribute?
If not, which URL helper class am I supposed to use to acquire the string data in the URL? Even if I have to parse the whole URL manually so be it, i just need to acquire that 3rd element in the URL as a string
Extremely n00b question im sure, but either im not finding this simple guide somewhere, or im not searching google correctly...
What you're missing is that the default route parameter name is "id". So you want to do this:
[HttpGet]
public ActionResult Search(String id)
{
ViewBag.ProvidedQuery = id;
return View();
}
If you don't want to use the variable name id, then you can modify your Route to look like this:
routes.MapRoute(
name: "Search",
url: "DataTypes/Search/{searchString}",
defaults: new { controller = "DataTypes", action = "Search",
searchString = UrlParameter.Optional });
If you don't want the string to be optional, then you can remove the last field from the defaults object.
you can use RouteTable.Routes.GetRouteData(new HttpContextWrapper(httpContext)) to get the routedata
String URL to RouteValueDictionary
You need to look at the routing in the Global.asax.cs. For example for your case you could add a route to the routes collection like this:
routes.MapRoute("Search",
"DataTypes/Search/{q}",
new { controller = "DataTypes", action = "Search" }
);
Then the q parameter will automatically get mapped to your action. The default controller mapping is likely mapping it to "id".
So, there are a wealth of Flex articles online about how to handle a .NET WebMethod that returns a DataSet or DataTable. Here is an example:
Handling web service results that contain .NET DataSets or DataTables
So, I know how to use result.Tables.<tablename>.Rows and the like. But what I cannot seem to figure out or find online is how to go the other direction - a method to pass objects or tables back to the .NET Webservice from Flex, without stooping to passing XML as a string, or making huge web service methods that have one parameter for each property/column of the object being stored. Surely others, smarter than I, have tackled this issue.
I am using ASP.NET 2.0 Typed DataSets, and it would be really nice if I could just pass one object or array of objects from Flex to the web service, populate my Typed DataTable, and do an Update() through the corresponding typed TableAdapter. My dream would be a [WebMethod] something like one of these:
public void SaveObject(TypedDataTable objToSave) { ... }
public void SaveObject(TypedDataSet objToSave) { ... }
I've had the typed datatables saving to the database, I know how to do that part and even a few tricks, but we had XML being passed back-and-forth as a string - eww. I'm trying to get to a more object-based approach.
The best object based approach is AMF. I assume its probably a bit late in your your development cycle to change your integration layer, but otherwise I dont know of a way to get around marshalling your object(s) back into XML or separating them out into their primitive components.
For .NET implementations of AMF check out:
FlourineFX(FOSS)
WebORB for .NET
Its amazing how easy things become once AMF is used, for example using the Mate MVC framework and an AMF call passing a complex object to the server looks something like this:
<mate:RemoteObjectInvoker instance="yourWebservice" method="saveComplexObject" showBusyCursor="true" >
<mate:resultHandlers>
<mate:CallBack method="saveComplexObjectSuccess" arguments="{[resultObject]}" />
</mate:resultHandlers>
<mate:faultHandlers>
<mate:MethodInvoker generator="{DataManager}" method="presentFault" arguments="{fault}" />
</mate:faultHandlers>
</mate:RemoteObjectInvoker>
With result and fault handlers being optional.
The direction I ended up going was close to what I hoped was possible, but is "hack-ish" enough that I would consider SuperSaiyen's suggestion to use AMF/ORM a better solution for new/greenfield projects.
For sake of example/discussion, let's say I am working with a Person table in a database, and have a typed DataSet called PeopleDataSet that has PersonTableAdapter and PersonDataTable with it.
READ would look like this in .NET web service:
[WebMethod]
public PeopleDataSet.PersonDataTable GetAllPeople() {
var adapter = new PersonTableAdapter();
return adapter.GetData();
}
... which in Flex would give you a result Object that you can use like this:
// FLEX (AS3)
something.dataProvider = result.Tables.Person.Rows;
Check out the link I put in the question for more details on how Flex handles that.
CREATE/UPDATE - This is the part I had to figure out, and why I asked this question. The Flex first this time:
// FLEX (AS3)
var person:Object = {
PersonID: -1, // -1 for CREATE, actual ID for UPDATE
FirstName: "John",
LastName: "Smith",
BirthDate: "07/19/1983",
CreationDate: "1997-07-16T19:20+01:00" // need W3C DTF for Date WITH Time
};
_pplWebSvcInstance.SavePerson(person); // do the web method call
(For handling those W3C datetimes, see How to parse an ISO formatted date in Flex (AS3)?)
On the .NET web service side then, the trick was figuring out the correct Type on the web method's parameter. If you go with just Object, then step into a call with a debugger, you'll see .NET figures it is a XmlNode[]. Here is what I figured out to do:
[WebMethod]
public int SavePerson(PeopleDataSet p) {
// Now 'p' will be a PeopleDataSet with a Table called 'p' that has our data
// row(s) (just row, in this case) as string columns in random order.
// It WILL NOT WORK to use PeopleDataSet.PersonDataTable as the type for the
// parameter, that will always result in an empty table. That is why the
// LoadFlexDataTable utility method below is necessary.
var adapter = new PersonTableAdapter();
var tbl = new PeopleDataSet.PersonDataTable();
tbl.LoadFlexDataTable(p.Tables[0]); // see below
// the rest of this might be familiar territory for working with DataSets
PeopleDataSet.PersonRow row = tbl.FirstOrDefault();
if (row != null) {
if (row.PersonID > 0) { // doing UPDATE
row.AcceptChanges();
row.SetModified();
}
else { // doing CREATE
row.CreationDate = DateTime.UtcNow; // set defaults here
row.IsDeleted = false;
}
adapter.Update(row); // database call
return row.PersonID;
}
return -1;
}
Now, the kluge utility method you saw called above. I did it as extension method, that is optional:
// for getting the Un-Typed datatable Flex gives us into our Typed DataTable
public static void LoadFlexDataTable(this DataTable tbl, DataTable flexDataTable)
{
tbl.BeginLoadData();
tbl.Load(flexDataTable.CreateDataReader(), LoadOption.OverwriteChanges);
tbl.EndLoadData();
// Probably a bug, but all of the ampersand (&) in string columns will be
// unecessarily escaped (&) - kluge to fix it.
foreach (DataRow row in tbl.Rows)
{
row.SetAdded(); // default to "Added" state for each row
foreach (DataColumn col in tbl.Columns) // fix & to & on string columns
{
if (col.DataType == typeof(String) && !row.IsNull(col))
row[col] = (row[col] as string).Replace("&", "&");
}
}
}