Develop Reference

Microsoft.Data.SQLite parameters not working

I'm building a database kiosk using Microsoft.Data.SQLite. I'm using parameterized queries when building commands. This WAS working until VS was having build problems, and after applying various updates (detailed below), my parameters are no longer being applied. Hardcoding the values into the commandText works.
I was previously using the basic
selectCommand.Parameters.Add("#Table", Table)
and I tried using a more explicit parameter. Here's the full command:
public static List<String> GetTables(string Table) // Get the Items in a Table
{
List<String> entries = new List<string>();
using (SqliteConnection db = new SqliteConnection(ConnectionString)) // the db
{
db.Open();
SqliteCommand selectCommand = new SqliteCommand("SELECT Item FROM #Table;", db);
selectCommand.Parameters.Add("#Table", SqliteType.Text).Value = Table;
SqliteDataReader query = selectCommand.ExecuteReader();
while (query.Read()) // while still reading data
{
entries.Add(query.GetString(0)); // add string to entries
}
db.Close();
}
return entries;
}
But the parameter still isn't being applied. Here's the full error:
SQLite Error 1: 'near "#Table": syntax error'.
at Microsoft.Data.Sqlite.SqliteException.ThrowExceptionForRC(Int32 rc, sqlite3 db)
at Microsoft.Data.Sqlite.SqliteCommand.<PrepareAndEnumerateStatements>d__62.MoveNext()
at Microsoft.Data.Sqlite.SqliteCommand.ExecuteReader(CommandBehavior behavior
at Microsoft.Data.Sqlite.SqliteCommand.ExecuteReader()
at DataAccessLibrary.DataAccess.GetTables(String Table)
at brogle.SelectionPage.<LoadItemGridContent>d__8.MoveNext()} Microsoft.Data.Sqlite.SqliteException
Clearly, #Table isn't being changed to the string Table, whose value is "Bulbs". (There is a table "Bulbs", and again, hardcoding that into the command works as expected.) Debugging shows that the command accepts the parameter #Table with value "Bulbs".
To solve my build issues (code analysis was throwing errors) I installed Microsoft.CodeAnalysis.FxCopAnalyzers, updated SQLitePCLRaw.bundle_winsqlite3 and Microsoft.NETCore.UniversalWindowsPlatform to latest stable, and updated VS to 15.9.7.
If you need more details about anything, I can provide. Thanks.

It's for parameters. You can not give table names that way, what you can do for workaround is this :
SqliteCommand selectCommand = new SqliteCommand("SELECT Item FROM "+Table, db);
For more detail please refer Retrieve data from the SQLite database official document.

Get output 'inserted' on update with Entity Framework

SQL Server provides output for inserted and updated record with the 'inserted' keyword.
I have a table representing a processing queue. I use the following query to lock a record and get the ID of the locked record:
UPDATE TOP (1) GlobalTrans
SET LockDateTime = GETUTCDATE()
OUTPUT inserted.ID
WHERE LockDateTime IS NULL
This will output a column named ID with all the updated record IDs (a single ID in my case). How can I translate this into EF in C# to execute the update and get the ID back?

Entity Framework has no way of doing that.
You could do it the ORM way, by selecting all the records, setting their LockDateTime and writing them back. That probably is not safe for what you want to do because by default it's not one single transaction.
You can span your own transactions and use RepeatableRead as isolation level. That should work. Depending on what your database does in the background, it might be overkill though.
You could write the SQL by hand. That defeats the purpose of entity framework, but it should be just as safe as it was before as far as the locking mechanism is concerned.
You could also put it into a stored procedure and call that. It's a little bit better than the above version because at least somebody will compile it and check that the table and column names are correct.

Simple Example #1 to get a data table:
I did this directly against the connection:
Changed the command.ExecuteNonQuery() to command.ExecuteReader()
var connection = DbContext().Database.Connection as SqlConnection;
using (var command = connection.CreateCommand())
{
command.CommandText = sql;
command.CommandTimeout = 120;
command.Parameters.Add(param);
using (var reader = command.ExecuteReader())
{
var resultTable = new DataTable();
resultTable.Load(reader);
return resultTable;
}
}
FYI, If you don't have an OUTPUT clause in your SQL, it will return an empty data table.
Example #2 to return entities:
This is a bit more complicated but does work.
using a SQL statement with a OUTPUT inserted.*
var className = typeof(T).Name;
var container = ObjContext().MetadataWorkspace.GetEntityContainer(UnitOfWork.ObjContext().DefaultContainerName, DataSpace.CSpace);
var setName = (from meta in container.BaseEntitySets where meta.ElementType.Name == className select meta.Name).First();
var results = ObjContext().ExecuteStoreQuery<T>(sql, setName, trackingEnabled ? MergeOption.AppendOnly : MergeOption.NoTracking).ToList();
T being the entity being worked on

INSERT object or UPDATE if it already exists using BulkCopy (C#, SQL)

I'm trying to update a table with a List<T>. I created an EnumExtension class and created a method which converts my Enumerable to a DataTable:
public static DataTable AsDataTable<T>(this IEnumerable<T> data)...
And then I started creating a method which should use BulkCopy to insert or update my table, using the enumerable. Right now, it's written like this:
public void BulkInsertOrUpdate(DatabaseEnum database, IEnumerable<Object> enumerable, string TableName)
{
var connection = this.GetSqlConnection(database);
var transaction = connection.BeginTransaction();
using (var bulkCopy = new SqlBulkCopy(connection, SqlBulkCopyOptions.Default, transaction))
{
bulkCopy.BatchSize = 100;
bulkCopy.DestinationTableName = TableName;
try
{
bulkCopy.WriteToServer(enumerable.AsDataTable());
}
catch (Exception)
{
transaction.Rollback();
connection.Close();
}
}
transaction.Commit();
}
(OBS: Method GetSqlConnection creates and opens my connection using the appropiate connection string.)
But I don't know how to create the update feature. Is there a simple way to do so, with an efficient code? I'm fond of BulkCopy, but I can try another method, hopefully not hurting my architecture (and, ultimately, I'll have to make this sacrifice if I can't find a way).
Thanks for your attention, I'm ready to answer doubts about my situation.

So I solved my problem (thanks #J-D).
I am basically using a temp table and inserting the data inside it. First I truncate it every time it's used:
connection.Query(database_name, sql_truncate_query);
Then I insert the data using the method I created previously:
connection.BulkInsert(database_name, ienumerable, table_name);
OBS: Changed the method name from BulkInsertOrUpdate to BulkInsert.
Later, I update my log table using a simple MERGE sql query:
INSERT [database].[table] (col1, col2)
SELECT col1, col2
FROM [database].[table2] t2
WHERE NOT EXISTS (SELECT col1 FROM [database].[table] t1 WHERE t1.col1= t2.col1);
OBS: My problem changed while I was developing, so I am no longer using the 'update' feature, I just need to check the existence of the row. Of course, you can write a code in which it updates the value if it's caught by the WHERE clause.
I don't know if it's the optimized way to resolve this problem, but it's certainly better than inserting or updating each row at a time.

MySQL and C# Getting data from DB and creating an associative array/object

I am new to C# and have been using PHP for Years.
The problem I am facing is that I want to create a method/function that will take an "sql query" as parameter and return whatever data is retrieved so that it can be used using the key/index/column_name.
What I have achieved
I have achieved is that I am able to access the data through index within the same function.
but I wont know the no. of columns that will return so I am unable to store it in an array.
Code
string ConnectionString = ConfigurationManager.ConnectionStrings["sqlcon"].ConnectionString;
MySqlConnection db;
db = new MySql.Data.MySqlClient.MySqlConnection(ConnectionString);
try
{
db.Open();
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = db;
cmd.CommandText = sql;
MySqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Console.WriteLine(rdr['areaId'].toString());
}
db.Close();
return true;
}
The problems
1. I do not know the number of Columns.
2. I cannot access the index or Column name.
I want to create an associative array of data with the column name as index and data as its data
EDIT
I am trying to build an application on C# using WPF with MySQL Database.

My first suggestion would be to use one of the micro ORMs like Dapper.net
This can be fetched via nuget. If you wish to retrieve an unknown array of data from a table, or number of tables, you could fetch it into an ExpandoObject and then enumerate over that. An example of looping over an ExpandoObject can be found here.
public Foo FetchSomeData(string query)
{
using (var cn = Connection)
{
var result = cn.Query(query);
//do something with result, and return it
return new Foo(result);
}
}
I'd have concerns about passing raw sql into the DB without at least checking it or using parameters as it could be a major security risk, especially if you allow users to generate the query and you don't vet it first.

Insert data from one SQL Database to a second one using C#

I dont know how to do this query in c#.
There are two databases and each one has a table required for this query. I need to take the data from one database table and update the other database table with the corresponding payrollID.
I have two tables in seperate databases, Employee which is in techData database and strStaff in QLS database. In the employee table I have StaffID but need to pull the PayrollID from strStaff.
Insert payrollID into Employee where staffID from strStaff = staffID from Employee
However I need to get the staffID and PayrollID from strStaff before I can do the insert query.
This is what I have got so far but it wont work.
cn.ConnectionString = ConfigurationManager.ConnectionStrings["PayrollPlusConnectionString"].ConnectionString;
cmd.Connection = cn;
cmd.CommandText = "Select StaffId, PayrollID From [strStaff] Where (StaffID = #StaffID)";
cmd.Parameters.AddWithValue("#StaffID", staffID);
//Open the connection to the database
cn.Open();
// Execute the sql.
dr = cmd.ExecuteReader();
// Read all of the rows generated by the command (in this case only one row).
For each (dr.Read()) {
cmd.CommandText = "Insert into Employee, where StaffID = #StaffID";
}
// Close your connection to the DB.
dr.Close();
cn.Close();

Assuminig, you want to add data to existing table, you have to use UPDATE + SELECT statement (as i mentioned in a comment to the question). It might look like:
UPDATE emp SET payrollID = sta.peyrollID
FROM Emplyoee AS emp INNER JOIN strStaff AS sta ON emp.staffID = sta.staffID

I have added some clarity to your question: the essential part is that you want to create a C# procedure to accomplish your task (not using SQL Server Management Studio, SSIS, bulk insert, etc). Pertinent to this, there will be 2 different connection objects, and 2 different SQL statements to execute on those connections.
The first task would be retrieving data from the first DB (for certainty let's call it source DB/Table) using SELECT SQL statement, and storing it in some temporary data structure, either per row (as in your code), or the entire table using .NET DataTable object, which will give substantial performance boost. For this purpose, you should use the first connection object to source DB/Table (btw, you can close that connection as soon as you get the data).
The second task would be inserting the data into second DB (target DB/Table), though from your business logic it's a bit unclear how to handle possible data conflicts if records with identical ID already exist in the target DB/Table (some clarity needed). To complete this operation you should use the second connection object and second SQL query.
The sample code snippet to perform the first task, which allows retrieving entire data into .NET/C# DataTable object in a single pass is shown below:
private static DataTable SqlReadDB(string ConnString, string SQL)
{
DataTable _dt;
try
{
using (SqlConnection _connSql = new SqlConnection(ConnString))
{
using (SqlCommand _commandl = new SqlCommand(SQL, _connSql))
{
_commandSql.CommandType = CommandType.Text;
_connSql.Open();
using (SqlCeDataReader _dataReaderSql = _commandSql.ExecuteReader(CommandBehavior.CloseConnection))
{
_dt = new DataTable();
_dt.Load(_dataReaderSqlCe);
_dataReaderSql.Close();
}
}
_connSqlCe.Close();
return _dt;
}
}
catch { return null; }
}
The second part (adding data to target DB/Table) you should code based on the clarified business logic (i.e. data conflicts resolution: do you want to update existing record or skip, etc). Just iterate through the data rows in DataTable object and perform either INSERT or UPDATE SQL operations.
Hope this may help. Kind regards,