I am having a hard time using ts field in cosmos/document db with c#. Is it just better to create another date time field and use that instead of ts? How to decide when to use ts vs a custom date time field?
_ts represents a Unix Epoch and marks the time of the document's last modification. When a document is created, it has the creation time, but if later on the document is updated, then _ts is updated with that time.
Effectively it means the last modified time of the document.
It depends on your use case if you can use it or you need a custom date field. For example, if your intent it to track when a document was created, then you can't use it, as the value will change if the document is modified. If your intent is to track the last modified time, it can work (depends on the precision you need and if a Unix Epoch fills that requirement, otherwise you would need your own custom field).
Here is the official reference of system properties: https://learn.microsoft.com/azure/cosmos-db/account-databases-containers-items#properties-of-an-item
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I am trying to use the DynamoDBAutoGeneratedTimestamp annotation for generating timestamps for when my records are last updated and when they are created. The annotation currently has 2 strategies, ALWAYS and CREATE.
My initial understanding was that the ALWAYS strategy should update the timestamp every time the record is changed, and the CREATE strategy should set the timestamp only when the record is created. The ALWAYS strategy appears to be working just fine in updating the timestamp each time the record changes; however, the CREATE strategy appears to be behaving exactly the same as the ALWAYS strategy (meaning the timestamp updates each time the record changes).
It is now my understanding that the CREATE strategy doesn't do that, and instead tells the record to generate a timestamp if you're going to write it to the database and the value of the field in the record to be written is null.
This causes the field with the CREATE strategy to always be updated if the record itself is ever updated.
So, are there any easy solutions to this? I could set it myself, of course, but I was wondering if there is some sort of option or config that is not known to me that would address this issue?
Example code:
#DynamoDBTable(tableName = "Foo")
public class Foo {
#DynamoDBAutoGeneratedTimestamp(strategy = DynamoDBAutoGenerateStrategy.CREATE)
private Date createdAt;
#DynamoDBAutoGeneratedTimestamp(strategy = DynamoDBAutoGenerateStrategy.ALWAYS)
private Date updatedAt;
}
I am using Firebase FireStore database for the first time and I have the following question.
I have created a calendar collection. This collection will contains document representing events that have to be shown into a Calendar implemented by an Angular application.
So I am defining the following fields for these documents:
id: int. It is a unique identifier of the specific document\event.
title: string. It is the event title.
start_date_time: string. It specifies the date and the time at which the event starts.
end_date_time: string. It specifies the date and the time at which the event ends.
And here I have some doubts:
Is the id field required? From what I know I will have the document UID that will ensure the uniqueness of the document. If not strongly required adopt an id field can be convenient have something like an auto increment field? (I know that I have to handle in some other way the auto increment because FireStore is not a relational DB and doesn't automatically handle it). For example I was thinking that can be useful to order my document from the first inserted one to the last inserted one.
It seems to me that FireStore doesn't handle DateTime field (as done for example by a traditional relational database). Is this assumption correct? How can I correctly handle my start_date_time and end_date_time fields? These field have to contains the date time used by my Angular application? So for example I was thinking that I can define it as string field and put into these fields values as 2020-07-20T07:00:00 representing a specific date and a specific time. It could be considered a valid approach to the problem or not?
Is the id field required?
No fields are required. Firestore is schema-less. The only thing a document requires is a string ID that is unique to the collection where it lives.
There is no autoincrement of IDs. That doesn't scale massively the way Firestore requires. If you need ordering, you will have to define that for yourself according to your needs.
In general, you are supposed to accept the randomly generated IDs that the Firebase client APIs will generate for you. Ordering is typically defined using a field in the document.
It seems to me that FireStore doesn't handle DateTime field
Firestore has a timestamp field type that stores moments in time to nanosecond precision. There is no need to store a formatted string, unless that's something you require for other reasons.
I've recently discovered firestore.Timestamp and so I tried to assign firestore.FieldValue.serverTimestamp(); to one and it didn't work. instead it says Type 'FieldValue' is not assignable to type 'Timestamp' which I would say is strange. Shouldn't serverTimestamp() be a Timestamp and not a FieldValue? What would be the purpose of firestore.Timestamp if not to save timestamps to Firestore? Is there a way to get a server timestamp that is compatible with firestore.Timestamp or should I be avoiding timestamps altogether, and just stick to firestore.FieldValue for all my dates?
serverTimestamp() just returns sentinel value that tells the Firestore server that it should use the current time on the server as the value for the field you're trying to set. It doesn't return an actual Timestamp object itself.
The reason why you'd use this is to make sure that dates are being set consistently on the server instead of depending on the clock being correct on the user's device.
If you want to know the current time on the device, just use the native date/time objects provided by the language or operating system.
In my app I use Firebase's childByAutoId() (swift) or .push() (web) to insert some data in the following format:
- events
- $autoId
- time:
- name:
- $autoId
- time:
- name:
Where $autoId are the randomly generated keys Firebase makes. time is the epoch time of when the data was pushed.
I want to allow users to modify each inserted entry's time. However, I want to keep the nodes under events sorted by their key and by time which Firebase naturally does when you use .push(). But if they modify the time so that it should actually be in a different order, the entries won't be sorted correctly.
Is there a way to generate an id by the modified time so that if it were inserted into events it would be in the right order? That way I could just delete the old entry and insert the new one while just duplicating the data.
Since the algorithm for Firebase's push IDs is well documented, you could easily modify the function to generate them based on a specific timestamp.
But I'd recommend instead keeping the necessary values as named properties for each child node. If you need to be able to sort by both creation and modification time, keep two separate properties. That way you won't have to depend on the behavior of the push IDs, but instead use more explicitly named properties to accomplish what you need.
I would like to find the date and time that any schema modification has taken place on a particular database. Modifications are things like tables or columns that have been created, altered, or dropped. It does not include any data that has been inserted, updated, or deleted.
The reason why I need this is because I am writing a .NET utility that depends heavily on the data returned from dbc.tables, dbc.columns, and dbc.indices. Since querying these views can be a very expensive operation, I want to read it all into custom business objects and then serialize the objects to an XML file stored on disk. This way, I can just deserialize the data when I need it unless the database's current_timestamp is greater than or equal to the datetime of the last schema change, at which point I'll refresh the local XML file with the updated schema.
LastAlterTimestamp - If it is equal to CreateTimestamp then object has not been modified since being created or replaced. It is updated when an attribute specific to that data dictionary object was updated.
For example, DBC.Databases.LastAlterTimestamp is not update when a child object (table, view, macro, stored procedure, function, etc.) is added, removed, or altered. It is updated in situations such as when the password, default role, profile, or account is changed.