Projecting search results lets you iterate over results that are more suitable for displaying search results and other types of listings. Also, because you are selecting a subset of the indexed data, only the required fields must be sent over the wire.
While the API supports returning instances of the actual type that is indexed (as long as it can be instantiated directly or by configuring the `
Client` conventions), you should return matching objects as instances of a different type, projecting them. As with LINQ, you do this with a `
This is a projection from a type named `
BlogPost` to a type named `
## Special methods
In general, if you invoke a method in a select expression, the method is invoked on the target object after fetching it from the search engine. In other words, if you changed the above example from `
Title = x.Title` to `
Title = x.Title.ToLower()`, the Title property is retrieved from the search engine, then `
ToLower` executes on the client.
However, some extension methods get special treatment when parsed in a select expression. One is the `
AsHighlighted` method. When using this, you can project fragments from the source text into the result object. For more information, see [Highlighting](🔗).
Another such method is `
AsCropped`. This lets you retrieve only the beginning of a longer text field. `
AsCropped` requires a single integer parameter, which controls the maximum length of the returned text. Unlike the `
SubString` method, no exception is thrown if the actual text is shorter than the requested maximum length. Here is a sample usage.
AsCropped` tries to crop text to the specified maximum length without separating words.
Because the method uses a script on the search engine side, the execution is slower than projections that do not use it.
The Optimizely Search & Navigation .NET client API's Select method is not as powerful as the in-memory LINQ version. Compared to most other LINQ providers, the method is quite powerful.
Select` method's primary limitation is that it does not support projecting from complex types, except for enumerables of non-complex types. In other words, in the example above, you could not project the full Author object. However, you could project individual fields from the Author object to a complex object.
Another limitation is that the `
Select` method can not project user-defined functions or delegates. When you use a user-defined function, it could end up requesting and loading the entire object, including the binary attachment fields and nested objects. Avoid using user-defined functions/delegates. Instead, explicitly declare the projection in the select expression.
In general, the `
Select` method works as expected if you are used to working with the LINQ equivalent and remember the limitation of not being able to project from complex objects. Below are more examples of the method.
And avoid to do something like this
## Select and the fluent API
In general, call the Select method _after_ calling searching and filtering methods. Those methods depend on the type you are searching for, rather than the type to which you are projecting search results.