Is it possible to easily query the state of an object from the JaVers repository as shadow/snapshot at a given time X?
Use case:
We have been logging changes to employee data with JaVers for 3 years. Now we would like a list of all employees who worked in the accounting department on 01.08.2019.
There is no such queries, Javers stores snapshots of objects and a snapshot is saved when you change an object.
So all you can do is to query for objects changed in a given period:
QueryBuilder.byClass(Employee).from(...).to(...)
Related
To the question "Save Differences with Entity ID" I found the following answer:
"For Entities, Id property cannot be null, so you need to map this class as ValueObject. If so,
Id property is treated as regular property and it not goes to GlobalId of this object."
My question is:
Why can't an entity be treated as NEW if the Id is NULL?
I have an object graph that is fetched from the database, and between two javers commits an entity is added to a list in the graph.
Two commits and in the second commit there is a new entity (Id NULL)
Get the change => exeption because Javers can't create a GlobalId.
I can get arround this by doing EntityManager - persist (creates Id:s), but I would like to avoid doing that. The present code may do a persist later or it just lets the transaction finish.
Because the Id is NULL, the entity is NEW. Would it be possible to generate a unigue temp Id (allow Id = NULL) to be able to create the GlobalId?
In the change list, the entity would be reported as NEW. No need to compare with earlier commits.
You should compare/commit your objects when they are fully initialized so when they have Ids.
An entity without Id can't be handled by JaVers for several reasons:
it can't be compared to other entity/version (diff algorithm is based on GlobalIds)
it can't be queried from JaVersRepository (queries use GlobalIds)
If you are using Hibernate, compare/commit your new objects after Hibernate assigns them Ids from sequences.
Another options:
don't use sequence-generated values as JaVers Id but some business identifiers
if an Entity doesn't have a business identifier you can generate UUID in a constructor and use it as JaVers id (and also database PK if you like)
Let me start by saying that I am indeed self-taught and I have no business trying to do what I am trying to do...However, I am combining two Access databases that track different information about the same projects (one tracks the proposal information for projects considered for selection and the other tracks budget information for those that are selected). The same projects have different IDs in each database. Each database has lookup fields (yeah, yeah, I know lookup fields are evil, but that is what I have). I want to update the values in the lookup fields for the related tables in the Budget DB to the ID fields for the same projects in the Project DB. Is there a way to write an update query to change the value in the project ID field of one table to the ID fields from another table?
Details: ProjectListTbl contains ProjectID field and the BudgetID field which refers to project ID from the Budget database (BDBID). I want the Reporting table values to change from the Budget Database ID (BDBProjectID) to the ProjectID from the ProjectListTbl. I have tried
UPDATE Reporting INNER JOIN ProjectListTbl ON ReportingTbl.BDBProjectID = ProjectListTbl.ProjectID SET ReportingTbl.BDBProjectID = [ProjectListTbl].[ProjectID], WHERE (((ReportingTbl.BDBProjectID)=DLookUp([ProjectListTbl].[ProjectID],[ProjectListTbl],[BudgetID]=[ReportingTbl]![BDBProjectID])));
I notice that in hibernate, it queries the child collections of entities an entity at a time. So, for example, I have a Person entity with a OneToMany relationship with PhoneNumber as well as a OneToMany relationship with EmailAddress. If I do a simple query on the Person entity that returns 1,000 people then hibernate will make 1,000 queries to EmailAddress and 1,000 queries to PhoneNumber. Let's forget about eager or lazy fetching for a minute and assume I will be accessing the phone and email collections of every person.
This seems like a naive implementation. Is there a simple way to change this so there is only 1 query into PhoneNumber and only 1 query into EmailAddress? These should be put into a map keyed by their Person foreign key so they are easily retrieved by the Person getter methods.
Any thoughts besides doing a brute force query into the session cache for emails and phone numbers BEFORE executing the Person query?
TIA, let me know if you need additional data.
Apart for doing the queries by yourself, you could simply enable batch fetching, as described in the documentation:
You can also enable batch fetching of collections. For example, if each Person has a lazy collection of Cats, and 10 persons are currently loaded in the Session, iterating through all persons will generate 10 SELECTs, one for every call to getCats(). If you enable batch fetching for the cats collection in the mapping of Person, Hibernate can pre-fetch collections:
I am creating an informatica workflow which can extract data from two tables of DB2 database and load into a temporary table. Suppose the two source tables name are Account (Parent) and Activities (Child). They have 1:M relationship. Means an Account can have many Activities (Account.PK = Activities.FK). Activities table has two columns- first 'Type' whose value could be 'Paid', 'Will-Pay' or 'Not-Paid'.And second column is 'Created_Date' datetime datatype, whenever you create new activity record, date and time would get stamp in this field. Now, condition to load data in temporary table is - "For an Account record, it would 1st check in Activities table for today's Paid activities (Type = Paid). If it finds more than one paid activities, then it would pick the Latest created one (Created_Date column) out of them. If there is no Paid activity record for the Account, then it would pick latest created 'Will-Pay' activity." Means, it should pick latest Paid activity for today (Sysdate) for an Account, if it is not present then only It will pick latest Will-pay activity for today. Please help me to understand how I can implement this logic in Informatica workflow and which transformations I should use and how? Thanks alot. Kindly help.
Best way to do it on SQL cause realize business logic on ETL it's not good. But if you insist it can be created by many ways. As example:
With SQL override
You can create 3 lookup transformation for Activities table with overrided SQL (and columns too) and one expression transformation for condition.
Lookup to find more than one 'paid' activities accounts
Lookup to find last 'paid' activity per account
Lookup to find last 'will pay' activity per account
Expression to return correct Activities key based from 1-3 lookup results
Without SQL override you need to recreate similar logic with filter, aggregator, joiner transformations.
I'm building a small financial system. Because of double-entry accounting, transactions always come in batches of two or more, so I've got a batch table and a transaction table. (The transaction table has batch_id, account_id, and amount fields, and shared data like date and description are relegated to the batch table).
I've been using basic vo-type models for each table so far. Because of this table structure, though, transactions will almost always be selected with a join on the batch table.
So should I take the selected records and splice them into two separate vo objects, or should I create a "shared" vo that contains both batch and transaction data?
There are a few cases in which batch records and/or transaction records are loaded individually, so they will each also have their associated vo class. Are there possible pitfalls down the road if I have "overlapping" vo classes like this?
The best approach is to tie models not to database tables, but to your views. E.g. if view has date field, then use "shared " view object (ideally even specific-to-the-view object), if view has only transaction info, use another object etc. It can be tedious, but separation of concerns will be worthy. Too much duplication can be remedied with reusing/inheriting when appropriate.