I am writing an app using the Realm.io database that will pull data from another, server database. The server database has some tables whose primary keys are composed of more than one field. Right now I can't find a way to specify a multiple column key in realm, since the primaryKey() function only returns a String optional.
This one works:
//index
override static func primaryKey() ->String?
{
return "login"
}
But what I would need looks like this:
//index
override static func primaryKey() ->[String]?
{
return ["key_column1","key_column2"]
}
I can't find anything on the docs on how to do this.
Supplying multiple properties as the primary key isn't possible in Realm. At the moment, you can only specify one.
Could you potentially use the information in those two columns to create a single unique value that you could use instead?
It's not natively supported but there is a decent workaround. You can add another property that holds the compound key and make that property the primary key.
Check out this conversation on github for more details https://github.com/realm/realm-cocoa/issues/1192
You can do this, conceptually, by using hash method drived from two or more fields.
Let's assume that these two fields 'name' and 'lastname' are used as multiple primary keys. Here is a sample pseudo code:
StudentSchema = {
name: 'student',
primaryKey: 'pk',
properties: {
pk: 'string',
name: 'string',
lastname: 'string',
schoolno: 'int'
}
};
...
...
// Create a hash string drived from related fields. Before creating hash combine the fields in order.
myname="Uranus";
mylastname="SUN";
myschoolno=345;
hash_pk = Hash( Concat(myname, mylastname ) ); /* Hash(myname + mylastname) */
// Create a student object
realm.create('student',{pk:hash_pk,name:myname,lastname:mylastname,schoolno: myschoolno});
If ObjectId is necessary then goto Convert string to ObjectID in MongoDB
Related
Simply put, is it possible to create a filter query where I reference a value stored in the row?
For example:
orm.em.findOne(Job, {
status: 'active',
startDate: {
$gt: '$anotherDateField'
}
}
My goal is to have a user-input defined filter (the status), but also only bring back certain rows where the start date is greater than another column's value.
You can use custom SQL fragment
orm.em.findOne(Job, {
status: 'active',
// expr helper allows to escape strict typing of the method, so we can use `em.raw()`
[expr('startDate')]: {
$gt: orm.em.raw('another_date_field') // this will have to be column name, not property name
}
}
Note that your em needs to be typed to the one exported from driver package to have access to the em.raw() method (if you work with orm instance, you need to type that to MikroORM<YourDriver> so orm.em can be properly typed).
https://mikro-orm.io/docs/entity-manager/#using-custom-sql-fragments
I have a table with a primary key and a sort key; since this is a composite key, I have multiple primary keys mapped with different sort keys.
How can I get all of the sort keys associated with a particular primary key?
I tried using the "Get" operation, but that seems to expect the sort key as well (even though these are what I'm looking for). I also looked at the "BatchGet" operation, but this is for multiple different keys, not for a single primary key with multiple different sort keys.
I tried to do "query" as well and wasn't successful, but I understand this less, so it's possible this is the solution -- is that the case? I am also aware that I could "scan" the entire database and specifically find all items with that particular primary key, but I'm looking to avoid this if possible.
I am working with JS and using this as a reference: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/DynamoDB/DocumentClient.html.
Thank you!
Query() is what you want...
Basically, you just query the table (or index) with a keycondition of HashKey = :hkey and leave off any AND of sort key conditions...
In the docs you linked to, there's a section for query modifying that example...
var params = {
TableName: 'Table',
KeyConditionExpression: 'HashKey = :hkey',
ExpressionAttributeValues: {
':hkey': 'key'
}
};
var documentClient = new AWS.DynamoDB.DocumentClient();
documentClient.query(params, function(err, data) {
if (err) console.log(err);
else console.log(data);
});
for some reason I want to use book.randomID as key in amazon DynamoDB table using java code. when i tried id added a new field in the item named "book.randomID"
List<KeySchemaElement> keySchema = new ArrayList<KeySchemaElement>();
keySchema.add(new KeySchemaElement().withAttributeName("conceptDetailInfo.conceptId").withKeyType(KeyType.HASH)); // Partition
and here is the json structure
{
"_id":"123",
"book":{
"chapters":{
"chapterList":[
{
"_id":"11310674",
"preferred":true,
"name":"1993"
}
],
"count":1
},
"randomID":"1234"
}
}
so is it possible to use such element as key. if yes how can we use it as key
When creating DynamoDB tables AWS limits it to the types String, Binary and Number. Your attribute book.random seems to be a String.
As long as it's not one of the other data types like List, Map or Set you should be fine.
Just going to AWS console and trying it out worked for me:
I'm using a third party package that defines a schema like this:
People.schema = new SimpleSchema({
firstName: {
type: String,
optional: false
}
//Many other fields defined...
});
I would like to modify it to have optional: true for the first name without changing the source code for the third party package.
I could use People.schema.pick to get a schema with all of the fields except the firstName, and then combine this with another schema with firstName as optional. But this method would require listing all of the fields in the schema in the pick function, which is tedious.
Is there a better way of accomplishing this?
I can edit the object simple schema creates just like any other object:
People.schema._schema.firstName.optional = true.
To override the field.
In RavenDB I can store objects of type Products and Categories and they will automatically be located in different collections. This is fine.
But what if I have 2 logically completely different types of products but they use the same class? Or instead of 2 I could have a generic number of different types of products. Would it then be possible to tell Raven to split the product documents up in collections, lets say based on a string property available on the Product class?
Thankyou in advance.
EDIT:
I Have created and registered the following StoreListener that changes the collection for the documents to be stored on runtime. This results in the documents correctly being stored in different collections and thus making a nice, logically grouping of the documents.
public class DynamicCollectionDefinerStoreListener : IDocumentStoreListener
{
public bool BeforeStore(string key, object entityInstance, RavenJObject metadata)
{
var entity = entityInstance as EntityData;
if(entity == null)
throw new Exception("Cannot handle object of type " + EntityInstance.GetType());
metadata["Raven-Entity-Name"] = RavenJToken.FromObject(entity.TypeId);
return true;
}
public void AfterStore(string key, object entityInstance, RavenJObject metadata)
{
}
}
However, it seems I have to adjust my queries too in order to be able to get the objects back. My typical query of mine used to look like this:
session => session.Query<EntityData>().Where(e => e.TypeId == typeId)
With the 'typeId' being the name of the new raven collections (and the name of the entity type saved as a seperate field on the EntityData-object too).
How would I go about quering back my objects? I can't find the spot where I can define my collection at runtime prioring to executing my query.
Do I have to execute some raw lucene queries? Or can I maybe implement a query listener?
EDIT:
I found a way of storing, querying and deleting objects using dynamically defined collections, but I'm not sure this is the right way to do it:
Document store listener:
(I use the class defined above)
Method resolving index names:
private string GetIndexName(string typeId)
{
return "dynamic/" + typeId;
}
Store/Query/Delete:
// Storing
session.Store(entity);
// Query
var someResults = session.Query<EntityData>(GetIndexName(entity.TypeId)).Where(e => e.EntityId == entity.EntityId)
var someMoreResults = session.Advanced.LuceneQuery<EntityData>(GetIndexName(entityTypeId)).Where("TypeId:Colors AND Range.Basic.ColorCode:Yellow)
// Deleting
var loadedEntity = session.Query<EntityData>(GetIndexName(entity.TypeId)).Where(e =>
e.EntityId == entity.EntityId).SingleOrDefault();
if (loadedEntity != null)
{
session.Delete<EntityData>(loadedEntity);
}
I have the feeling its getting a little dirty, but is this the way to store/query/delete when specifying the collection names runtime? Or do I trap myself this way?
Stephan,
You can provide the logic for deciding on the collection name using:
store.Conventions.FindTypeTagName
This is handled statically, using the generic type.
If you want to make that decision at runtime, you can provide it using a DocumentStoreListner