I want to modify a SQL query using Calcite. For example
SELECT values FROM data to
SELECT values as v FROM data
I could access SqlNode of select identifier using SqlVisiter implementation.
public Object visit(SqlCall sqlCall) {
SqlNodeList selectList = ((SqlSelect) sqlCall).getSelectList();
for (SqlNode sqlNode : selectList) {
System.out.println(sqlNode.toString());
}
Now what should I do to update SqlNode?
The SqlNode objects in the select list will be instances of SqlIdentifier in this case. So you'll have to cast sqlNode to a SqlIdentifier and then you can call .setName(0, "NEW_NAME"). After this, you call unparse on the original root node to get the new query back.
Related
I want to retrieve all rows matched on multiple partial prase against with a column. My situation can be explained as following raw sql:
SELECT *
FROM TABLENAME
WHERE COLUMN1 LIKE %abc%
OR COLUMN1 LIKE %bcd%
OR COLUMN1 LIKE %def%;
Here, abc, bcd, def are array elements. i.e: array('abc','bcd','def'). Is there any way to write code passing this array to form the above raw sql using cakephp 3?
N.B: I am using mysql as DBMS.
probably you can use Collection to create a proper array, but I think a foreach loop will do the job in the same amount of code. So here is my solution supposing $query stores your Query object
$a = ['abc','bcd','def'];
foreach($a as $value)
{
$or[] = function ($exp, $q) use ($value) {
return $exp->like('column1', '%'.$value.'%');
};
}
$query->where(['or' => $or]);
you could also use orWhere() but I see it will be deprecated in 3.6
When using sql select I need a counter for my sequence row like this:
var result = from d in data
select new[]
{
Convert.ToString((count++))
};
but this syntax gives the following error message:
An expression tree may not contain an assignment operator Vehicle.app..NETCoreApp,Version=v1.0
When using LINQ (e.g. from x in data select { ... }) the expression in the selection is translated into a SQL statement and executed in the database. How would an assignment like count++ work in a database? I think you're better off with selecting the records from the database and apply the sequence number on the in memory list of data rather than on the queryable collection which represents the database. For example:
var data = (from d in data select new { ... }).ToList();
var result = data.Select(new { id = Convert.ToString(count++), ... }).ToList();
I refer to this example: Return selected specified columns
Quote:
If BlobDetails isn't the LINQ entity, then you can do it directly:
var qry = from b in dc.Blobs
orderby b.RowVersion descending
select new BlobDetails {
Id = b.Id, Size = b.Size,
Signature = b.Signature, RowVersion = b.RowVersion};
return qry.ToList();
I see that they are selecting specific column in a query through the ORM-tool LINQ TO SQL.
Critics of ORM-tools say that, if I remember correctly, that ORM-tools select and return entire objects from the table, and limits the options of selecting only specific columns as one can do through classic SQL-programming. Of course, I have my doubts about that when I see this example, but nevertheless, I still keep asking myself the question: Does the database return only the selected columns, or does it return the entire objects, leaving the column-filtering to the ORM-tool?
From this example, they also have a class called Blobdetails:
public class BlobDetails
{
public int Id { get; set; }
public string Signature { get; set; }
public int Size { get; set; }
public System.Data.Linq.Binary RowVersion { get; set; }
}
Do I need to create my own classes everytime I only wish to select a few columns from a table through LINQ?
You don't need to create new classes to select few columns from a table. You can use anonymous types for that.
var qry = from b in dc.Blobs
orderby b.RowVersion descending
select new { b.Id, b.Size, b.Signature, b.RowVersion};
return qry.ToList();
Only selected columns are transferred. There is no difference between using plain SQL and using LINQ to SQL. When you are executing LINQ query, it is converted to plain SQL and executed. Then result is mapped to your objects.
You can use SQL Server Profiler to see what query was generated and executed on server. Also you can use LINQPad to see what SQL will be generated from your query. In your case query will be same either you use BlobDetails or anonymous object:
SELECT [t0].[Id], [t0].[Size], [t0].[Signature], [t0].[RowVersion]
FROM [Blobs] AS [t0]
ORDER BY [t0].[RowVersion] DESC
when you do projections LINQ does indeed only select those columns and there is nothing preventing you from materializing it however you want. So in your example code
select new BlobDetails
{
Id = b.Id,
Size = b.Size,
Signature = b.Signature,
RowVersion = b.RowVersion
};
Only b.id, b.size, b.signature, & b.rowversion are selected. You can verify this with sql profiler or your debugger, I seem to recall there is also a function you can call on the datacontext to get the last query that was ran.
I think that the answer to your first question is already in the POST you mentioned. However...
If your BlobDetails is not LINQ entity you can simply use it in your select statement to define (shrink) your projection attributes. For example:
var qry = from b in dc.Blobs
select new BlobDetails { Id = b.Id, Size = b.Size }
would compile to SQL query like SELECT Id, Size FROM Blob ....
But if BlobDetails is LINQ entity you will need to use that AsEnumerable() hack otherwise you will get NotSupportedException: Explicit construction of entity type in query is not allowed.
var qry = from b in dc.Blobs.AsEnumerable()
select new BlobDetails { Id = b.Id, Size = b.Size }
Edit
As #Chris Pitman stated in his comment this AsEnumerable() approach could create serious bottleneck, beacause the whole table would be loaded in memory before applying the projection. So it is not recommended!
To your second question:
You will need to create custom class for objects that you want use easily outside the scope of the method. Properties of an anonymous object are visible only in the scope, where they have been declared and anonymous objects can be cast only to type object.
So if you want to return anonymous objects from method the return type would has to be an enumerable of object or dynamic as #xeondev stated in his comment.
There's no need to create your own classes, you can return an anonymous type. You can write something like this
var qry = from b in dc.Blobs
orderby b.RowVersion descending
select new {
Id = b.Id, Size = b.Size,
Signature = b.Signature, RowVersion = b.RowVersion};
return qry.ToList();
Although the signature of the method should look to something like this
public IEnumerable<object> GetItems()
or
public dynamic GetItems()
So if you are going to use the result of linq query in outer scope like you example suggest, it is highly recommended you create your own classes.
When you map a table to an object, every property created corresponds to one db column.
I want to execute a db function on a column before it gets mapped to the property, so the property gets the value returned by the db function, and not the column
I was trying to achieve that by Expression property of ColumnAttribute (as in the example below), so instead of BirthDate the usrFn_UTCToLocalTime(BirthDate) is returned
but it does not seem to be working and still gets pure value of the column.
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage = "_BirthDate", DbType = "DateTime", UpdateCheck = UpdateCheck.Never, Expression = "dbo.usrFn_UTCToLocalTime(BirthDate)")]
public System.Nullable<System.DateTime> BirthDate
{
get
{
return this._BirthDate;
}
}
I have also modified the DBML XML as in:
other post on stackoverflow
but also without result.
Is that possible by using LINQ or do I have to overwrite a getter which costs roundtrip to the server?
According to the Remarks section on this MSDN page, the Expression property of the ColumnAttribute is used when calling CreateDatabase, so it won't work the way you intend unless you created your database with Linq to Sql.
You can create a Linq query that selects the various columns and calls the db function in one statement like this (based on MSDN example):
var qry = from person in db.Persons
select new {
FirstName = person.FirstName,
LastName = person.LastName,
BirthDate = person.BirthDate,
Dob = db.usrFn_UTCToLocalTime(person.BirthDate)
};
This projects into an anonymous type, but you could use a non-anonymous type as well. For the sake of the example, I've got a table named Person with FirstName, LastName, and BirthDate columns, and a user defined scalar function named usrFn_UTCToLocalTime. The sql statement sent to the server is:
SELECT [t0].[FirstName], [t0].[LastName], [t0].[BirthDate], CONVERT(DateTime,[dbo].[usrFn_UTCToLocalTime]([t0].[BirthDate])) AS [Dob]
FROM [dbo].[Person] AS [t0]
As I was suggesting in the question, for now I have overwritten the get method so I have:
get
{
using (var context = DB.Data.DataContextFactory.CreateContext())
{
return context.usrFn_UTCToLocalTime(_BirthDate);
}
//return this._BirthDate;
}
But with every access to the property, roundtrip is made - which is not my intention but gives a proper result.
I leave the question still open
I'm using Modeshape and modeshape-connector-jdbc-metadata. I want to get all nodes representing tables in the storage. That nodes have [mj:catalog] mixin type.
I'm querying storage using next code:
public List getDatabases() throws RepositoryException {
// Obtain the query manager for the session ...
QueryManager queryManager = dbSession.getWorkspace().getQueryManager();
// Create a query object ...
Query query = queryManager.createQuery("SELECT * FROM [mj:table]"
, Query.JCR_SQL2);
// Execute the query and get the results ...
QueryResult result = query.execute();
// Iterate over the nodes in the results ...
NodeIterator nodeIter = result.getNodes();
List stringResult = new ArrayList();
while (nodeIter.hasNext()) {
stringResult.add(nodeIter.nextNode().getName());
}
return stringResult;
}
But it always returns empty list.
I also tried to query using next queries:
SELECT unst.*, tbl.* FROM [nt:unstructured] AS unst
JOIN [mj:table] AS tbl ON ISSAMENODE(unst,tbl)
SELECT * FROM [nt:unstructured] WHERE [jcr:mixinTypes] = [mj:table]
But result remains the same.
What I'm doing wrong?
Thank you for any help.
There is a known issue that the database metadata nodes are not indexed automatically. A simple workaround is to cast the JCR Session's getWorkspace() instance to org.modeshape.jcr.api.Workspace (the public API for ModeShape's workspace) and call the reindex(String path) method and passing in the path to the database catalog node (or an ancestor if desired).