SelectQueryFilterService.cs

using System.Collections.Generic;
using System.Linq;
using DevExpress.Data.Filtering;
using DevExpress.DataAccess.Sql;
using DevExpress.DataAccess.Web;

namespace QueryFilterServiceApp.Services {
    public class SelectQueryFilterService : ISelectQueryFilterService {
        readonly int studentId;

        public SelectQueryFilterService(IUserService userService) {
            studentId = userService.GetCurrentUserId();
        }

        public CriteriaOperator CustomizeFilterExpression(
            SelectQuery query, CriteriaOperator filterExpression) 
        {
            List<CriteriaOperator> filters = new List<CriteriaOperator>();

            if(query.Tables.Any(x => x.ActualName == "Students")) {
                filters.Add(new BinaryOperator
                    (new OperandProperty("Students.ID"), 
                    new OperandValue(studentId), 
                    BinaryOperatorType.Equal));
            }

            if(query.Tables.Any(x => x.ActualName == "Enrollments")) {
                filters.Add(new BinaryOperator
                    (new OperandProperty("Enrollments.StudentID"), 
                    new OperandValue(studentId), 
                    BinaryOperatorType.Equal));
            }

            if(query.Tables.Any(x => x.ActualName == "Reports")) {
                filters.Add(new BinaryOperator
                    (new OperandProperty("Reports.StudentID"), 
                    new OperandValue(studentId), 
                    BinaryOperatorType.Equal));
            }

            if(!object.ReferenceEquals(filterExpression, null)) {
                filters.Add(filterExpression);
            }

            var result = filters.Any() ? new GroupOperator(GroupOperatorType.And, filters) : null;
            return result;
        }
    }
}