breezeJS custom predicates - breeze

Question

I want to write a slightly complex query, so I wonder if there is a way to provide a custom function as the predicate of a where clause.
For example, it would be nice if we could do something like:
var myArray = [1, 2, 3];
var filter = function (person) {
return elementExists(person.id, myArray);
};
EntityQuery.from('persons').toType('Person')
.where(filter);
Looking at the source code I realized that such capability is not present in the latest version of BreezeJS (i might be wrong).
I just wonder if breeze supports anything similar to that.

Answer 1

On the client side you should be able to find out if the element exists by checking the length of the return.
var getItems = function (runId, tankId, topicId) {
var localquery = EntityQuery.from("Items")
.using(manager);
var p1 = new breeze.Predicate("runId", "eq", runId);
var p2 = breeze.Predicate("tankId", "eq", window.app.vm.tanks.activetank());
var p3 = breeze.Predicate("topicId", "eq", topicId);
var p4 = breeze.Predicate("topicId", "eq", app.Topics.Growth_Topic);
var pred;
var runId = p1._value;
var tankId = p2._value;
// If the third parameter exists, add it to your complex predicate
// adding a specific Topic to the predicate
// Otherwise only add the General topic
if (p4)
pred = breeze.Predicate.or([p3, p4]);
else
pred = breeze.Predicate.or(p3);
var newpred = breeze.Predicate.and([p1, p2, pred]);
// newpred is now querying for a specific runId and tankId and (p3 or p4) if p4 exists
// otherwise it is querying for runId and tankId or (p3)
// So look in the local metadataStore first
var queryb = localquery.where(newpred);
var results = manager.executeQueryLocally(queryb);
// If we do have it locally use it
if (results.length) {
window.app.vm.Items.Items(results);
}
// otherwise get it from the database
else {
var query = EntityQuery
.from("Items")
.where(newpred);
// return the promise from breeze
return manager.executeQuery(query)
.then(function (data) {
// check to see if the call to the webapi controller returned any data
if (data.length > 0) {
// stick it into the viewmodel it to your viewmodel
window.app.vm.Items.Items(data.results);
return "element exists";
} else {
return "element does not exist";
}
})
.fail(queryFailed);
}
};
This example is quite a bit more complicated that you requested, so cut out the parts you do not want to simplify your query. I am showing you here how to get both an "and" and an "or" into your query. I am also showing how to check the local metadataStore, to see if the item is there before going to the server.
If the item does not exist and you want to create it, be careful about your thread timing and wrap the object creation in a promise before you do something like navigating to another page to show the new item. The navigation may be faster than the creation function and the new item may not be bound into your viewmodel yet by knockout, so it might show up blank on the new page. That will drive you crazy for quite a while.