Implementing the server filter

When there is a need to show a certain subset of data on the grid depending on a user’s role, the server filter can be used. It allows filtering the data right on the application’s back end, so Flexmonster Pivot receives and shows only the part of the data that meets filtering conditions.

In this guide, we describe the concept of the server filter, its structure, and the example of the server filter implementation:

• The general idea of the server filter
• Example of a server filter
• The server filter structure

The general idea of the server filter

The main advantage of the server filter is that it can be used as a data access management tool. Using the server filter, Flexmonster.DataServer.Core.dll will filter the data based on the user role received from Flexmonster Pivot.

Here is one of the possible server-side filtering implementations:

1. When Flexmonster Pivot sends a request for data to the server, the user’s role can be included in the request headers with customizeAPIRequest. This method allows editing the headers before the request is sent to the server.
2. After the Data Server accepts the request, the request headers can be read. Depending on the received role, the DLL can apply the appropriate filter to the data.
3. The resulting subset of data is sent to Flexmonster Pivot. The component gets the dataset specific to the current user.

To see how the server filter can be implemented, refer to the Example section.

Example of a server filter

To make the server filter’s implementation easier, we designed a sample ASP.NET Core application using Flexmonster.DataServer.Core.dll. This application contains an example of a server filter, which can be viewed in the FlexmonsterAPIController.cs file.

To create a new ASP.NET Core application with the Data Server or embed the DLL in the existing project, refer to the guide on Flexmonster.DataServer.Core.dll.

Defining user roles on the server side

In the sample, the data is filtered based on the user’s region token sent by the component via request headers. A special dictionary defines which subset of data should correlate to the received token. The dictionary contains all possible region tokens and field members corresponding to them:

private static Dictionary<string, List<object>> _userPermissions =
new Dictionary<string, List<object>>()
{
    /* a user with the "AdminToken" token will see
    the report on all the countries */
    {"AdminToken", null },

    /* a user with the "EuropeToken" token will see
    details about Germany and France */ 
    {"EuropeToken", new List(){ "Germany","France" } },

    /* a user with the "AmericaToken" token will see
    highlights about USA and Canada */
    {"AmericaToken", new List(){ "USA","Canada" } },

    /* a user with the "AustraliaToken" token will see
    info about Australia */
    {"AustraliaToken", new List(){ "Australia" } },
};

Defining the server filter

In the sample project, the server filter is defined in a separate function. First, a user token is read from the request headers, and then, depending on that token, the filter is applied:

private ServerFilter GetServerFilter()
{
    // get the user token from the request headers
    HttpContext.Request.Headers.TryGetValue("UserToken", out StringValues userRole);
    if (userRole.Count == 1)
    {
        // create a server filter
        ServerFilter serverFilter = new ServerFilter();
        // specify a field to filter
        serverFilter.Field = new Field() { 
            UniqueName = "Country", 
            Type = ColumnType.stringType
        };
        // include the members that correspond to the user token
        serverFilter.Include = _userPermissions[userRole[0]];
        return serverFilter;
    }
    return null;
}

To learn more about the server filter’s parameters and their types, see the server filter structure. 

Applying the server filter

After the filter is specified, it is passed as a parameter to GetMembers() and GetAggregatedData() methods, for example:

public MembersResponse PostMembers([FromBody]MembersRequest request)
{
    var response = _apiService.GetMembers(request, GetServerFilter());
    return new JsonResult(response);
}

The server filter structure

The server filter has the following structure:

public class ServerFilter
{
    public Field Field { get; set; }
    public List<object> Include { get; set; }
    public List<object> Exclude { get; set; } 
}

Below is a detailed description of the filter parameters:

• Field – Field. A field to filter. If a non-existent field is specified, Flexmonster.DataServer.Core.dll throws the exception.
• Include – List<object>. Field members to include in the server’s response.
• Exclude – List<object>. Field members to exclude from the server’s response.

Here is an example of how the server filter can be created:

ServerFilter serverFilter = new ServerFilter();
serverFilter.Field = new Field() {
    UniqueName = "Country",
    Type = ColumnType.stringType
};
serverFilter.Include = new List<object>(){ "USA", "Canada" };

What’s next?

You may be interested in the following articles:

• Implementing the custom parser
• Referring the Data Server as a DLL
• Implementing the API controller
• DLL configurations reference