This package provides a [FixOdataQuery] action filter attribute which resolves LINQ compatibility issues between ASP.NET Web API OData and NHibernate. This is currently maintained against the nightly OData builds and the NHibernate 3.4 trunk due to additional compatibility issues between their stable releases.

Usage

Install the NuGet package and apply the attribute to your queryable Web API controller action:

[Queryable, FixOdataQuery]
public IQueryable<Item> Get()
{
	return ...;
}

Or apply it automatically to all queryable responses in global.asax (if you've configured the QueryableAttribute filter globally):

protected void Application_Start()
{
	GlobalConfiguration.Configuration.Filters.Add(new FixOdataQuery());
}

See the Samples section for more details.

Implementation details

The attribute rewrites queries which aren't supported by NHibernate.

Nullable conditions

OData generates Nullable<bool> conditions, which are rewritten into regular bool conditions.

For example, the following query:

/items/?$filter=Parent/ID+eq+61+and+ID+eq+11

...is converted by ASP.NET Web API OData into an expression tree like this:

(.If ($$it.Parent == null) {
	null
} .Else {
	(System.Nullable`1[System.Int32])($$it.Parent).ID
} == (System.Nullable`1[System.Int32])61 AndAlso (System.Nullable`1[System.Boolean])($$it.ID == 11)) == .Constant<System.Nullable`1[System.Boolean]>(True)

If this query is passed to NHibernate, it will crash because it doesn't support Nullable<bool> operands for AndAlso. The attribute rewrites the query into this:

(.If ($$it.Parent == null) {
	null
} .Else {
	(System.Nullable`1[System.Int32])($$it.Parent).ID
} == (System.Nullable`1[System.Int32])61 AndAlso $$it.ID == 11) == True

SubstringOf, StartsWith, EndsWith methods

OData generates fairly complex expression trees for all these methods.

For example, the following query

/items?$filter=substringof('parent', Name) eq true

...is converted by ASP.NET Web API OData into an expression tree like this:

.Lambda #Lambda1<System.Func`2[Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent,System.Boolean]>(Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent $$it)
{
	(.If (
		$$it.Name == null | .Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]).TypedProperty ==
		null
	) {
		null
	} .Else {
		(System.Nullable`1[System.Boolean]).Call ($$it.Name).Contains(.Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]).TypedProperty)
	} == (System.Nullable`1[System.Boolean]).Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Boolean]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Boolean]).TypedProperty)
	== .Constant<System.Nullable`1[System.Boolean]>(True)
}

NHibernate fails to parse this into an SQL query. The FixStringMethodsVisitor will transform it into the following:

.Lambda #Lambda1<System.Func`2[Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent,System.Boolean]>(Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent $$it)
{
	(System.Nullable`1[System.Boolean]).Call ($$it.Name).Contains(.Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.String]).TypedProperty)
	== (System.Nullable`1[System.Boolean]).Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Boolean]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Boolean]).TypedProperty
}

...and now NHibernate can parse it and generate the proper SQL queries.

Component mappings

OData generates a null check when querying a property of a component, which is not necessary since NHibernate will map it directly to a column. If the component has more than 3 properties mapped, NHibernate fails to create a query from the LINQ expression.

For example, the following query

/items?$filter=Parent/Two eq 61

...is converted by ASP.NET Web API OData into an expression tree like this:

.Lambda #Lambda1<System.Func`2[Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent,System.Boolean]>(Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent $$it)
{
	(.If ($$it.Component == null) {
	 null
	} .Else {
	 (System.Nullable`1[System.Int32])($$it.Component).Two
	} == (System.Nullable`1[System.Int32]).Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Int32]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Int32]).TypedProperty)
	== True
}

NHibernate fails to parse this into an SQL query. The FixComponentNullCheckVisitor will transform it into the following:

.Lambda #Lambda1<System.Func`2[Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent,System.Boolean]>(Pathoschild.WebApi.NhibernateOdata.Tests.Models.Parent $$it)
{
	(System.Nullable`1[System.Int32])($$it.Component).Two
	 == (System.Nullable`1[System.Int32]).Constant<System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Int32]>(System.Web.Http.OData.Query.Expressions.LinqParameterContainer+TypedLinqParameterContainer`1[System.Int32]).TypedProperty)
}

...and now NHibernate can parse it and generate the proper SQL queries.

Links

Contributing

Feel free to fork this repo, write a test for your use-case or bug and fix it.

Included in the repository are StyleCop and ReSharper settings file. If possible, please use them appropriately to easily follow guidelines for style in the project. Use tabs and git config core.autocrlf true as well!

Contributors

See the CONTRIBUTORS file.

Samples

A project named WebApi.NHibernate-OData.Sample exists with usage examples.

There are two controllers for the two ways to use it.

The parents controller uses an attribute to modify the output along with the EnableQueryAttribute of Web API 2.

The children controller call the fix directly in the action method if specific handling is necessary.

http://localhost:15394/parents?$filter=not%20substringof(%27wot%27,%20Name)%20and%20startswith(Name,%20%27parent%2061%27)&$select=Id,Name
http://localhost:15394/children?$filter=Parent/Component/Two eq 61