I have a table the only has an Id column in SQL. It is an Auto-Increment column. It is used to keep track of a booking number sequence to be sent to an outside system. In SQL I use this to insert a new record:
insert into bookingnumbers default values
I would like to use entity framework and get the Next available Id. I have tried this:
private async Task<long> GetNextBookingNumberAsync()
{
BookingNumbers bookingNumber = default;
GhanemContext.BookingNumbers.Add(bookingNumber);
await GhanemContext.SaveChangesAsync();
return bookingNumber.Id;
}
However, booking number is just null and I get:
ArgumentNullException: Value cannot be null. Parameter name: entity
Any help would be greatly appreciated!
Related
I need to check if a book rating for specific book from specific person exists.
If it does update it, if it doesnt create it.
I am getting a whole bunch of wrong errors for 9th 10th.... 12th parameter missing while I count only 8
My mariaDB version is 10.5.8-MariaDB.
My code:
const createBookRate = async (userId, bookId, rate) => {
const sql = `
SELECT IF(EXISTS( SELECT * from rates WHERE rates.users_id=? AND rates.books_id=? ),
UPDATE rates SET rates.rate=? WHERE rates.users_id=? AND rates.books_id=?,
INSERT INTO rates(users_id, books_id, rate))
VALUE (?,?,?,?,?,?,?,?);
`
const { insertId } = await pool.query(sql, [userId, bookId, rate, userId, bookId, userId, bookId, rate])
const rateEntry = await getBookRate(insertId)
return rateEntry
}
You cannot perform an UPDATE or an INSERT inside the IF clause of a SELECT statement, those must be performed separately.
To perform this in a safe manner, use a transaction and first lock the selected row with SELECT ... FOR UPDATE, then either UPDATE or INSERT it and finally COMMIT the transaction.
If the table has a primary key, you can use INSERT ... ON DUPLICATE KEY UPDATE to either insert the row or update it, depending on whether it exists or not. This allows everything to be done in one step without having to first select the affected rows.
I am fairly new in this realm and any help is appreciated
I have a table in Dynamodb database named Tenant as below:
"TenantId" is the hash primary key and I have no other keys. And I have a field named "IsDeleted" which is boolean
Table Structure
I am trying to run a query to get the record with specified "TenantId" while it is not deleted ("IsDeleted == 0")
I can get a correct result by running the following code: (returns 0 item)
var filter = new QueryFilter("TenantId", QueryOperator.Equal, "2235ed82-41ec-42b2-bd1c-d94fba2cf9cc");
filter.AddCondition("IsDeleted", QueryOperator.Equal, 0);
var dbTenant = await
_genericRepository.FromQueryAsync(new QueryOperationConfig
{
Filter = filter
}).GetRemainingAsync();
But no luck when I try to get it with following code snippet (It returns the item which is also deleted) (returns 1 item)
var queryFilter = new List<ScanCondition>();
var scanCondition = new ScanCondition("IsDeleted", ScanOperator.Equal, new object[]{0});
queryFilter.Add(scanCondition);
var dbTenant2 = await
_genericRepository.LoadAsync("2235ed82-41ec-42b2-bd1c-d94fba2cf9cc", new DynamoDBOperationConfig
{
QueryFilter = queryFilter,
ConditionalOperator = ConditionalOperatorValues.And
});
Any Idea why ScanCondition has no effect?
Later I also tried this: (throw exception)
var dbTenant2 = await
_genericRepository.QueryAsync("2235ed82-41ec-42b2-bd1c-d94fba2cf9cc", new DynamoDBOperationConfig()
{
QueryFilter = new List<ScanCondition>()
{
new ScanCondition("IsDeleted", ScanOperator.Equal, 0)
}
}).GetRemainingAsync();
It throws with: "Message": "Must have one range key or a GSI index defined for the table Tenants"
Why does it complain about Range key or Index? I'm calling
public AsyncSearch<T> QueryAsync<T>(object hashKeyValue, DynamoDBOperationConfig operationConfig = null);
You simply cant query a table only giving a single primary key (only hash key). Because there is one and only one item for that primary key. The result of the Query would be that still that single item, which is actually Load operation not Query. You can only query if you have composite primary key in this case (Hash (TenantID) and Range Key) or GSI (which doesn't impose key uniqueness therefore accepts duplicate keys on index).
The second code attempts to filter the Load. DynamoDBOperationConfig's QueryFilter has a description ...
// Summary:
// Query filter for the Query operation operation. Evaluates the query results and
// returns only the matching values. If you specify more than one condition, then
// by default all of the conditions must evaluate to true. To match only some conditions,
// set ConditionalOperator to Or. Note: Conditions must be against non-key properties.
So works only with Query operations
Edit: So after reading your comments on this...
I dont think there conditional expressions are for read operations. AWS documents indicates they are for put or update operations. However, not being entirely sure on this since I never needed to do a conditional Load. There is no such thing like CheckIfExists functionality as well in general. You have to read the item and see if it exists. Conditional load will still consume read throughput so your only advantage would be only NOT retrieving it in other words saving the bandwith (which is very negligible for single item).
My suggestion is read it and filter it in your application layer. Dont query for it. However what you can also do is if you very need it you can use TenantId as hashkey and isDeleted for range key. If you do so, you always have to query when you wanna get a tenant. With the query you can set rangeKey(isDeleted) to 0 or 1. This isnt how I would do it. As I said, would just read it and filter it at my application.
Another suggestion thing could be setting a GSI on isDeleted field and writing null when it is 0. This way you can only see that attribute in your table when its only 1. GSI on such attribute is called sparse index. Later if you need to get all the tenants that are deleted (isDeleted=1) you can simply scan that entire index without conditions. When you are writing null when its 0 dynamoDB wont put it in the index at the first place.
How to query range key programmatically in DynamoDB, I am using .Net AWSSDK ,I am able to query on Hash key with below code :
GetItemRequest request = new GetItemRequest
{
TableName = tableName
};
request.Key = new Dictionary<string,AttributeValue>();
request.Key.Add("ID",new AttributeValue { S = PKValue });
GetItemResponse response = client.GetItem(request);
Please suggest,
Thanks in advance.
There are two kinds of primary key in DynamoDB: Hash-only or Hash-Range.
In the above code I guess your table is Hash-only and you use the hash key to retrieve an element with hashkey equals to PKValue.
If your table is in H-R schema and you want to retrieve a specific element with a hashKey and rangeKey, you can reuse the above code and in addition, add the {"RangeKey", new AttributeValue } into your your request.KEY
On the other hand, query means a different thing in DynamoDB. Query will return you a list of rows sorted in some order.
I need help in ydn db.
My issue is as follows: How can I fetch records by 2 conditions?
In sql it would be:
"SELECT * FROM store WHERE name='Test' AND cool=1;"
Currently my attempt looks like this:
var keyRange = ydn.db.KeyRange.bound(['Test', true]);
var db = DB.getDatabase();
database
.get('personStore', 'name, cool', keyRange)
.done(function(records) {
console.log(records);
});
Thanks in advance :-)
As discussed in this page, you can use compound index (as you did) or key joining. If you index ['name', 'cool'], you should be able to query by ydn.db.KeyRange.only(['Test', 1]). Note that boolean is not a valid key. Even if cool is boolean value, you have to index as integer value. But my suggestion is index only name and, just query name and filter out cool value on the result set.
I have created windows service for data-insertion.Time interval is one min.After one min, data insert into table.Data get inserted into table at multiple time.I don't want to that,only one time.How to do that?May I need to check in database wether entry is there or nor if not add.
You can use this query before inserting the data.
IF EXISTS(SELECT * FROM dbo.YourTable WHERE Name = #Name)
RETURN
-- here, after the check, do the INSERT
You might also want to create a UNIQUE INDEX on your Name column to make sure no two rows with the same value exist:
CREATE UNIQUE NONCLUSTERED INDEX UIX_Name
ON dbo.YourTable(Name)
Hope this help you.
//You can do like this in ur code
if (ChkRecordExist() == true)
{
//Do nothing
}
else
{
// insert operation
}
protected bool ChkRecordExist()
{
//here logic for record exist or not.
//if record is exist return true else return false
}