C#•3y ago

How do I 'build' a QUERY with EF Core?

Essentially I had an endpoint that can take multiple query string params, most are optional, so I want to check first if the query parameter exists - then if it does "add" it to the query. This keeps to be sending me errors and doesn't feel efficient; have I missed something?

12 Replies

Angius•3y ago

var query = _context.Things.AsQueryable();

if (data.Name is {} name) {
    query = query.Where(t => t.Name == name);
}
if (data.Age is > 0 age) {
    query = query.Where(t => t.Age == age);
}
if (data.SortBy is not null) {
    query = query.OrderBy(a => a.Something);
}

var things = await query.ToListAsync();

var query = _context.Things.AsQueryable();

if (data.Name is {} name) {
    query = query.Where(t => t.Name == name);
}
if (data.Age is > 0 age) {
    query = query.Where(t => t.Age == age);
}
if (data.SortBy is not null) {
    query = query.OrderBy(a => a.Something);
}

var things = await query.ToListAsync();

Like this

BreadOP•3y ago

Ahh, so build the queryable; then it is airquoteleft

called

when you .ToListAsync()

Angius•3y ago

Yep

BreadOP•3y ago

Interesting!

Angius•3y ago

.ToListAsync(), .FirstOrDefaultAsync(), CountAsync() etc. are where the query gets resolved

BreadOP•3y ago

So I guess my current impl, is just executing the query then I'm transforming the shape of the data based on my signty

Angius•3y ago

Your current code doesn't really do anything Since the query doesn't get modified in place You just call the .Where() on the query... and discard it

BreadOP•3y ago

Angius•3y ago

Good:

query = query.Where(...);

query = query.Where(...);

Bad:

query.Where(...);

query.Where(...);

BreadOP•3y ago

Ahhhhh! So just update the query with it

Angius•3y ago

All those methods — besides the ones that resolve the query — return an IQueryable, they're not void Yeah

BreadOP•3y ago

Thanks!

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How do I 'build' a QUERY with EF Core?