实体框架性能问题

Question

I'm having a problem where the below query is taking around 700ms to execute. It's in a loop and gets called 100+ times so it's taking forever.

Model:

public class ReleaseDates
{
    public int Id { get; set; }
    public string MovieName { get; set; }
    public string Country { get; set; }
    public DateTime ReleaseDate { get; set; }
    public string AlternateSource { get; set; }
}

Query:

public async Task<List<ReleaseDates>> GetReleaseDatesAsync(string movieName)
{
    return await Db.ReleaseDates.Where(x => x.MovieName == movieName && string.IsNullOrEmpty(x.AlternateSource)).ToListAsync();
}

Any suggestions how to speed this up?

Answer 1

Get rid of the loop. That's the problem. You're sending a lot of queries to database.

Store all the movie names that you're searching for in a list and do a contains there.

public async Task<List<ReleaseDates>> GetReleaseDatesAsync(List<string> movieNames)
{
    //movie names that you're searching for - movieNames

    return await Db.ReleaseDates.Where(x => movieNames.Contains(x.MovieName) && string.IsNullOrEmpty(x.AlternateSource)).ToListAsync();

}

If you want to get the release dates for "Ant Moon", "GodZippa", "SuperWan", your list will contain these strings and this is it.

Some further reading: http://blogs.msdn.com/b/alexj/archive/2009/03/26/tip-8-writing-where-in-style-queries-using-linq-to-entities.aspx

Answer 2

Create a index on your movie name field. Also, catch the query through profiler and exec it in Sql Management Studio with Show Plan enabled. It will give you some insights to optimize the query performance.