How can I build Entity Framework queries dynamically?

I'm quite new to Entity Framework and I have a question about filtering data.

I have two various Log entities, they are: DiskLog and NetworkLog. These entities both are derived from Log entity. Here is some code from my C# app:

public class Log { ... }
public class DiskLog : Log { ... }
public class NetworkLog : Log { ... }

public enum LogType
{
    NotInitialized = 0,
    Disk,
    Network
}

public List<Log> GetWithFilter(
    Guid userKey, 
    int nSkip, 
    int nTake, 
    DateTime dateFrom = DateTime.MinValue, 
    DateTime dateTo = DateTime.MaxValue, 
    LogType logType = LogType.NotInitialized, 
    int computerId = 0)
{
    // need to know how to optimize ...

    return ...
}

Of course, I already have working app and database tables created. What I want to do is to make function GetWithFilter work. I have several execution ways there:

1. if logType == LogType.Disk && computerId <= 0 (it means there is no need to use computerId parameter in the query, select DiskLog entities only)

2. if logType == LogType.Disk && computerId > 0 (means I have to use computerId parameter, select DiskLog entities only)

3. if logType == LogType.NotInitialized && computerId <= 0 (no need to use computerId and logType, just select all the entities, DiskLog and NetworkLog)

4. if logType == LogType.NotInitialized && computerId > 0 (select all types of logs for specified computer)

5. if logType == LogType.Network && computerId <= 0 (select all NetworkLog entities)

6. if logType == LogType.Network && computerId > 0 (select all NetworkLog entities for specified computer)

As you can see, there are plenty of available options. And I got to write 6 queries li