Is it possible to build dynamic queries for Amplify Datastore? - amazon-web-services

Question

I am looking to create a query-builder for my Amplify Datastore.
The function should process an an array of conditions, that need to be applied to the query and return the according Predicate.
This is easily done, if there is only one filter, but I would like to be able to process any amount of filters.
My goal is to be able to write the queries like so:
Datastore.query(Post, *queryBuilder(filters)*)
Where I can pass an array of filters with a filter looking like this:
filter = {
connector: 'or' |
property: rating
predicate: 'gt'
value: 4
}
and the query builder returns the Predicate in the below mentioned format.
I have tried to chain and return multiple functions in the query builder, but I was not able to figure out a pattern for how to create the correct predicate function.
For reference, this is how queries are built according to the docs: https://docs.amplify.aws/lib/datastore/data-access/q/platform/js#predicates
const posts = await DataStore.query(Post, c => c.rating("gt", 4));
and for multiple conditions:
const posts = await DataStore.query(Post, c =>
c.rating("gt", 4).status("eq", PostStatus.PUBLISHED)
);

Answer 1

Let's say we have the model:
type Post #model{
id: ID!
category: String
city: String
content: String
}
And we want to query & filter by city and category by a dynamic amount of variables. Then we can make a function as such on our script:
const fetchData = async props => {
/*
More configurable wrapper for Datastore.query calls
#param props: {model: Model, criteria: [{fieldId, predicate, value}]}.
*/
try {
let criteria;
if (props.criteria && typeof props.criteria === 'object') {
criteria = c => {
props.criteria.forEach(item => {
const predicate = item.predicate || 'eq';
c[item.fieldId](predicate, item.value);
});
return c;
};
} else {
criteria = props.criteria;
}
return await DataStore.query(props.model, criteria);
} catch (e) {
throw new Error(e);
}
}
So now if we want to execute this we can pass the parameters:
// where Post = models.Post
const myResult = fetchData({model: Post, criteria: [
{ fieldId: 'category',
predicate: 'eq',
value: 'news'
},
{
fieldId: 'city',
predicate: 'eq',
value: 'SomeCityName'
}]
})
Unfortunately I do not know of a way to also query linked relationships as you would using a direct graphQL api query while using DataStore and this method I presented only uses implicit AND between criteria.

Answer 2

I don't know if this has changed since you asked the question but, based on the documents, it looks like multiple conditions have an implicit and, but you can explicitly chain them with or/and/not:
const posts = await DataStore.query(Post, c => c.or(
c => c.rating("gt", 4).status("eq", PostStatus.PUBLISHED)
));