Putting multiple values in a WHERE clause in Azure Mobile Services

问题

I'm trying to figure out how to put multiple values into a WHERE clause; this is the kind of thing you'd use a IN clause for in SQL.

My current code:

if (Log.Count() == 1)
{
    items = itemTable
        .Where(Item => Item.id == Log[0].i_id)
        .ToCollectionView();
}
else if (Log.Count() == 2)
{
    items = itemTable
        .Where(Item => Item.id == Log[0].i_id || Item.id == Log[1].i_id)
        .ToCollectionView();
}
else if (Log.Count() == 3)
{
    items = itemTable
        .Where(Item => Item.id == Log[0].i_id || Item.id == Log[1].i_id || Item.id == Log[2].i_id)
        .ToCollectionView();
}

It's pretty nasty. I can't find a way to put multiple values into that WHERE clause without a big if statement. Any ideas?

回答1:

I faced the same issue. Using Any or Contains as others have suggested gave me a Not Supported Exception. I posted on the Azure Mobile Services forum and was told that IN is not supported yet. They advised I use an extension method which worked perfectly for me. Below is the code I used.

 public static class Extensions
{
    public async static Task<List<T>> In<T>(this IMobileServiceTable<T> table, List<int> ids)
    {
        var query = new StringBuilder("$filter=(");
        for (int i = 0; i < ids.Count; i++)
        {
            query.AppendFormat("id eq {0}", ids[i]); //don't forget to url escape and 'quote' strings
            if (i < ids.Count - 1)
            {
                query.Append(" or ");
            }
        }
        query.Append(")");
        var list = await table.ReadAsync(query.ToString());
        var items = list.Select(i => MobileServiceTableSerializer.Deserialize<T>(i)).ToList();
        return items;
    }
}

Your list can be populated by calling the extension method like this:

FavoriteJokesList = await jokeItemTable.In(favoriteJokeIds);

Source: http://social.msdn.microsoft.com/Forums/en-US/azuremobile/thread/b573ff6c-1f6b-4846-b44d-4678e3d26f66

回答2:

Try this instead:

items = itemTable
    .Where(Item => Log.Any(logItem => logItem.i_id == Item.id))
    .ToCollectionView();

Edit: (in response to the "not supported exception")

You can try this alternative to see if the backend supports it:

var ids = Log.Select(logItem => logItem.i_id).ToList();
var items = itemTable
    .Where(Item => ids.Contains(Item.id))
    .ToCollectionView();

回答3:

items = itemTable.Where(Item => Log.Any(i => i.i_id == Item.id)).ToCollectionView();

回答4:

Just for the record, in the newest Version of the Azure Mobile Service SDK (1.0), this works:

var ids = Log.Select(logItem => logItem.i_id).ToList();
var items = await itemTable
.Where(Item => ids.Contains(Item.id))
.ToCollectionAsync();

来源：https://stackoverflow.com/questions/15172995/putting-multiple-values-in-a-where-clause-in-azure-mobile-services

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