The below code is transforming OData filter to LINQ, but it is SQL dependent. I want to connect it with GraphDB, i.e., it should extract entities from graph, but I'm unable to understand how to proceed.
public IQueryable<AssetGroup> Get (ODataQueryOptions<AssetGroup> query)
{
var items = query.ApplyTo(from i in _db.Assets select i);
return (IQueryable < AssetGroup >) items;
}
Related
I am new to Web API, Entity Framework and OData. I asked a similar question in another forum but haven't gotten a relevant response.
We have a OData compliant web api service for use in Salesforce. We have a custom complex query in Oracle that we need to expose.
I am not sure how to use a custom query like we want to also allow for odata parameter filtering to occur? ($filter, $top, $skip, etc) For example, when a $filter is used i want to apply that filter to the custom query and then send it back to the database to have it return the result set. How can i do this?
The issue i seem to have is that I can see the parameters as they come in but they are not translating to the query being passed to oracle. It seems that it will fire the query returning the full result set and then apply the parameters. This is very slow as the result set is very large.
I am hoping 2 figure out 2 things
1. How can i use custom sql and apply odata parameters to the underlying query?
2. When using EF or a custom query, how can i apply odata parameters to the query so that when the query is sent to the database that the $filter parameter, for example, is included in the query? I don't want the full result returned then apply the filter.
Can anyone give me some pointers on how to make this happen?
private static ODataValidationSettings _validationSettings = new ODataValidationSettings();
//public IHttpActionResult GetName()
//{ }
// GET: odata/ShareData
[ODataRoute("Orders")]
[EnableQuery(PageSize = 50)]
public IHttpActionResult GetOrders(ODataQueryOptions<Orders> queryOptions)
{
// validate the query.
try
{
queryOptions.Validate(_validationSettings);
}
catch (ODataException ex)
{
return BadRequest(ex.Message);
}
try
{
string connectionString = ConfigurationManager.ConnectionStrings["DNATestConnectionString"].ConnectionString;
var items = GetDataItems(connectionString);
return Ok<IEnumerable<Orders>>(items);
}
catch (Exception ex)
{
return StatusCode(HttpStatusCode.InternalServerError);
}
}
#region Load Data Methods
private static List<Orders> GetDataItems(string connectionString)
{
List<Orders> items = new List<Orders>();
using (OracleConnection con = new OracleConnection(connectionString))
{
con.Open();
using (OracleCommand cmd = con.CreateCommand())
{
cmd.CommandText = "select po_header_id, segment1, vendor_id, vendor_site_id from po_headers_all where vendor_id=4993";
using (OracleDataReader rdr = cmd.ExecuteReader())
{
while (rdr.Read())
items.Add(ToOrders(rdr));
}
}
}
return items;
}
private static Orders ToOrders(OracleDataReader rdr)
{
Orders data = new Orders();
data.VENDOR_ID = ToInt32(rdr, "VENDOR_ID");
data.VENDOR_SITE_ID = ToInt32(rdr, "VENDOR_SITE_ID");
data.PO_HEADER_ID = ToInt32(rdr, "PO_HEADER_ID");
data.SEGMENT1 = Convert.ToString(rdr["SEGMENT1"]);
return data;
}
private static int ToInt32(OracleDataReader rdr, string name)
{
int index = rdr.GetOrdinal(name);
return rdr.IsDBNull(index) ? 0 : Convert.ToInt32(rdr[index]);
}
#endregion
I don't think this is possible.
How can i use custom sql and apply odata parameters to the underlying query?
As far as I'm aware, you can't. The whole point of the OData library is that it needs to work off an IQueryable. By using custom SQL in a string like you have in your example, you can't combine it with the OData parameters that are being passed in.
One approach would be to have your custom SQL in a SQL view, then add the SQL view to your EF model in the same way as you would add a table - it will be represented as a DbSet just like tables are.
You can then get an IQueryable to represent the dataset and then apply the OData parameters as follows:
public IHttpActionResult GetOrders(ODataQueryOptions<OrdersView> queryOptions)
{
IQueryable<OrdersView> allData = // ... get the DbSet from entity framework...
// this will apply the OData query to the data set and only pull the data you want from the database
var filteredResults = queryOptions.ApplyTo(allData) as IQueryable<OrdersView>;
return Ok<IQueryable<OrdersView>>(filteredResults);
}
How can a LINQ query be written to return all Accounts where the account number is not in a List?
The list is going to be pulled from an excel document.
private bool GetAccounts()
{
List<String> accountIds = new List<String>();
accountIds.Add( "[unknown]");
var query = from accounts in context.AccountSet where !accountIds.Contains(accounts.AccountNumber) select accounts;
}
It does not have to be a List.
EDIT
This is what happens when the above query runs - Is this CRM's fault?
I don't believe you can via linq. Here is the where clause limitations from the SDK.
where =>
The left side of the clause must be an attribute name and the right side of the clause must be a value. You cannot set the left side to a constant. Both the sides of the clause cannot be constants.
Supports the String functions Contains, StartsWith, EndsWith, and Equals.
You can get around these limitations by using QueryExpression or FetchExpressions. The query you want would look like this using QueryExpression. The only thing I would mention is if you are expecting a lot of record (5000+ I believe) you will most likely need to implement paging for your function as well.
private static IEnumerable<Account> GetAccounts(IOrganizationService proxy)
{
List<String> accountIds = new List<String>(new string[]{"654321", "12345"});
var results = proxy.RetrieveMultiple(new QueryExpression(Account.EntityLogicalName)
{
ColumnSet = new ColumnSet("accountid", "name", "accountnumber"),
Criteria = new FilterExpression()
{
Conditions = { new ConditionExpression("accountnumber", ConditionOperator.NotIn, accountIds) }
}
});
return results.Entities.Select(x=> x.ToEntity<Account>());
}
Consider the following (working) query. It returns an entire SharePoint row, then I get the value I (really wanted) from the row. How can I return only that value?
var ctx = new webservc.MyDataContext(new Uri("http://uri"));
ctx.Credentials = CredentialCache.DefaultCredentials;
var query = from c in ctx.MyList orderby c.ValIWant descending select c;
foreach (webservc.MyListItem item in query.Take(1))
{
return (int)item.ValIWant;
}
return 0;
I tried doing "select c.ValIWant" but I get an exception as a result. I cannot use LINQ stuff such as ".Max()" because SharePoint does not support it in the WCF Web Services, so I'm trying to stick to simple queries like the one I have above.
I'm converting an entity object to a model that can be passed around my application without the extra overhead (As well as generating a couple of extra fields for the view etc.
public IEnumerable<PageModel> GetAllPages()
{
var AllPageO = _session.All<Page>();
IList<PageModel> RetO = new List<PageModel>();
foreach (var AP in AllPageO)
{
RetO.Add(new PageModel(AP));
}
return RetO.AsEnumerable();
}
Can this be converted to a Linq Query, the below does work I get the error
Server Error in '/' Application. Only
parameterless constructors and
initializers are supported in LINQ to
Entities.
public IEnumerable<PageModel> GetAllPages()
{
var AllPageO = _session.All<Page>();
var RetO = from EntityO in AllPageO select new PageModel(EntityO);
return RetO;
}
Resharper actually converts the firt loop into this, which also fails with the same error.
IList<PageModel> RetO = PageO.Select(AP => new PageModel(AP)).ToList();
Thats because entity framework is trying to convert optimize your projection expression into sql.
The easy fix is to enumerate the results before the projection:
var RetO = from EntityO in AllPageO.ToList() select new PageModel(EntityO);
I am using the latest Nhibernate and i have a linq query to return just 1 column. so I can't use for example IQueryable as there is no entity class - i am returning only 1 column. But return to IQueryable Non Generic version doesn't provide the ToList method
Here is the method
public IQueryable GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new
{
Group = c.Code
}).Distinct();
}
}
Of course if i do this (see below) i get the ToList method on my IQueryable
public IQueryable<Client> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c;
}
}
The problem being is that i need to do DISTINCT and use only 1 column.
Any ideas, i am at a loss
Thanks in advance
EDIT
When i look at the type that is returned via IQueryable it is
{NHibernate.Linq.NhQueryable<<>f__AnonymousType6>}
and looking under the base class of what is returned i see an exception
Expression type 10005 is not supported by this SelectClauseVisitor.
Wouldn't the following work?
public IQueryable<X> GetCode() // X = the type of Client.Code
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c.Code).Distinct();
}
}
The problem here is not just that you can't call ToList on a non-generic IQueryable, but that the entire result is untyped, so you cannot read the Code property of each element either. (This can be worked around with C# 4's dynamic type, but that's not really what you want here.)
In your case, I don't see why you really need to construct an anonymous type just to return a distinct sequence of Code values renamed as Group. Returning the field's value should be sufficient.
If you'd need to return more than just one column, you should create an explicit type, rather than using an anonymous type, so you can say
public IQueryable<ClientGroupAndSomething> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new ClientGroupAndSomething
{
Group = c.Code,
...
}).Distinct();
}
}