As a Contains implementation, I am using a bit tweaked method written by Andy Dent to query my realm database:
private IQueryable<Entry> FilterEntriesByIds(IQueryable<Entry> allEntries, int[] idsToMatch)
{
// Fancy way to invent Contains<>() for LINQ
ParameterExpression pe = Expression.Parameter(typeof(Entry), "Entry");
Expression chainedByOr = null;
Expression left = Expression.Property(pe, typeof(Entry).GetProperty("Id"));
for (int i = 0; i < idsToMatch.Count(); i++) {
Expression right = Expression.Constant(idsToMatch[i]);
Expression anotherEqual = Expression.Equal(left, right);
if (chainedByOr == null)
chainedByOr = anotherEqual;
else
chainedByOr = Expression.OrElse(chainedByOr, anotherEqual);
}
MethodCallExpression whereCallExpression = Expression.Call(
typeof(Queryable),
"Where",
new Type[] { allEntries.ElementType },
allEntries.Expression,
Expression.Lambda<Func<Entry, bool>>(chainedByOr, new ParameterExpression[] { pe }));
return allEntries.Provider.CreateQuery<Entry>(whereCallExpression);
}
It all works just fine as long as I pass less than 2-3K of ids, when I go with larger amounts the app just crashes with what seems to be a stackoverflow exception.
My first thought to solve this was to break the query into chunks and later combine the results, but the Concat and Union methods do not work on these realm IQueryables, so, how else can I merge such chunked results? Or is there any other workaround?
I can't just convert the results to a List or something and then merge, I have to return realm objects as IQueryable<>
The call stack:
=================================================================
Native Crash Reporting
=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================
No native Android stacktrace (see debuggerd output).
=================================================================
Basic Fault Address Reporting
=================================================================
Memory around native instruction pointer (0x7c326075c8):0x7c326075b8 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0x7c326075c8 fd 7b bb a9 fd 03 00 91 a0 0b 00 f9 10 0e 87 d2 .{..............
0x7c326075d8 10 d0 a7 f2 90 0f c0 f2 b0 0f 00 f9 10 00 9e d2 ................
0x7c326075e8 f0 d5 a9 f2 90 0f c0 f2 b0 13 00 f9 a0 a3 00 91 ................
=================================================================
Managed Stacktrace:
============================
=====================================
at Realms.QueryHandle:GroupBegin <0x00000>
at Realms.RealmResultsVisitor:VisitCombination <0x0007f>
at Realms.RealmResultsVisitor:VisitBinary <0x003f7>
at System.Linq.Expressions.BinaryExpression:Accept <0x00073>
at System.Linq.Expressions.ExpressionVisitor:Visit <0x00087>
at Realms.RealmResultsVisitor:VisitCombination <0x000d7>
at Realms.RealmResultsVisitor:VisitBinary <0x003f7>
at System.Linq.Expressions.BinaryExpression:Accept <0x00073>
at System.Linq.Expressions.ExpressionVisitor:Visit <0x00087>
at Realms.RealmResultsVisitor:VisitCombination <0x000d7>
at Realms.RealmResultsVisitor:VisitBinary <0x003f7>
at System.Linq.Expressions.BinaryExpression:Accept <0x00073>
at System.Linq.Expressions.ExpressionVisitor:Visit <0x00087>
at Realms.RealmResultsVisitor:VisitCombination <0x000d7>
at Realms.RealmResultsVisitor:VisitBinary <0x003f7>
at System.Linq.Expressions.BinaryExpression:Accept <0x00073>
at System.Linq.Expressions.Ex
pressionVisitor:Visit <0x00087>
UPD
I found the exact number of elements after which this error gets thrown: 3939, if I pass anything larger than that, it crashes.
I'm not a database expert, just have worked at varying levels (inc Realm) usually on top of someone's lower-level engine. (The c-tree Plus ISAM engine or the C++ core by the real wizards at Realm).
My first impression is that you have mostly-static data and so this is a fairly classical problem where you want a better index generated up front.
I think you can build such an index using Realm but with a bit more application logic.
It sounds a bit like an Inverted Index problem as in this SO question.
For all the single and probably at least double-word combinations which map to your words, you want another table that links to all the matching words. You can create those with a fairly easy loop that creates them from the existing words.
eg: your OneLetter table would have an entry for a that used a one-to-many relationship to all the matching words in the main Words table.
That will delivery a very fast Ilist you can iterate of the matching words.
Then you can flip to your Contains approach at 3 letters or above.