I'm using Linq2NHibernate 3.0 with sybase ASE 15.
My first problem was that the dialect does not support limits ("select top 5 ..."). As a consequence, I made a custom dialect overriding those methods :
public override bool SupportsLimit
{
get { return true; }
}
public override bool SupportsLimitOffset
{
get { return true; }
}
public override bool SupportsVariableLimit
{
get
{
return true;
}
}
public new int GetLimitValue(int offset, int limit)
{
//TOOK FROM ANOTHER DIALECT
if (limit == int.MaxValue)
return int.MaxValue;
if (UseMaxForLimit)
return GetOffsetValue(offset) + limit;
return limit;
}
public override SqlString GetLimitString(SqlString sql, SqlString offset, SqlString limit)
{
//TOOK FROM ANOTHER DIALECT EXCEPT THAT I CALL ANOTHER CUSTOM CLASS
}
NOTE : I USE ANOTHER CLASS TO PASS THE LIMIT VALUE INTO GetLimitString USING LOCKS (I did not find a better alternative)
I thought it worked fine but GetLimitString is only called once, as a result, if I change the limit value, it is not taken into account.
So, my problem can be solved two ways: you have a better custom dialect for Sybase, or you know why GetLimitString is only called once.
Thanks in advance
Related
I am using Spring JDBC and some nice Java 8 lambda-syntax to execute queries with the JDBCTemplate.
The reason for choosing Springs JDBCTemplate, is the implicit resource-handling that Spring-jdbc offers (I do NOT want a ORM framework for my simple usecase's).
My problem is that I want to debug the whole SQL statements with their parameters. Spring prints the SQL by default but not the parameters. Therefor I have subclassed the JDBCTemplate and overridden a query-method.
An example usage of the JDBCTemplate:
public List<Product> getProductsByModel(String modelName) {
List<Product> productList = jdbcTemplate.query(
"select * from product p, productmodel m " +
"where p.modelId = m.id " +
"and m.name = ?",
(rs, rowNum) -> new Product(
rs.getInt("id"),
rs.getString("stc_number"),
rs.getString("version"),
getModelById(rs.getInt("modelId")), // method not shown
rs.getString("displayName"),
rs.getString("imageUrl")
),
modelName);
return productList;
}
To get hold of the parameters I have, as mentioned, overridden the JDBCTemplate class. By doing a cast and using reflection I get the Object[] field with the parameters from an instance of ArgumentPreparedStatementSetter.
I suspect this implementation could potentially be dangerous, as the actual implementation of the PreparedStatementSetter may not always be ArgumentPreparedStatementSetter (Yes I should do an instanceOf check). Also, the reflection code may not be as elegant, but that is besides the point now though :).
Here's my custom implementation:
public class CustomJdbcTemplate extends JdbcTemplate {
private static final Logger log = LoggerFactory.getLogger(CustomJdbcTemplate.class);
public CustomJdbcTemplate(DataSource dataSource) {
super(dataSource);
}
public <T> T query(PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor<T> rse)
throws DataAccessException {
if(log.isDebugEnabled()) {
ArgumentPreparedStatementSetter aps = (ArgumentPreparedStatementSetter) pss;
try {
Field args = aps.getClass().getDeclaredField("args");
args.setAccessible(true);
Object[] parameters = (Object[]) args.get(aps);
log.debug("Parameters for SQL query: " + Arrays.toString(parameters));
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new GenericException(e.toString(), e);
}
}
return super.query(psc, pss, rse);
}
}
So, when I execute the log.debug(...) statement I would also like to have the original SQL query logged (same line). Has anyone done something similar or are there any better suggestions as to how this can be achieved?
I do quite a few queries using this CustomJDBCTemplate and all my tests run, so I think it may be an acceptable solution of for most debug purposes.
Kind regards,
Thomas
I found a way to get the SQL-statement, so I will answer my own question :)
The PreparedStatementCreator has the following implementation:
private static class SimplePreparedStatementCreator implements PreparedStatementCreator, SqlProvider
So the SqlProvider has a getSql() method which does exactly what I need.
Posting the "improved" CustomJdbcTemplate class if anyone ever should need to do the same :)
public class CustomJdbcTemplate extends JdbcTemplate {
private static final Logger log = LoggerFactory.getLogger(CustomJdbcTemplate.class);
public CustomJdbcTemplate(DataSource dataSource) {
super(dataSource);
}
public <T> T query(PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor<T> rse)
throws DataAccessException {
if(log.isDebugEnabled()) {
if(pss instanceof ArgumentPreparedStatementSetter) {
ArgumentPreparedStatementSetter aps = (ArgumentPreparedStatementSetter) pss;
try {
Field args = aps.getClass().getDeclaredField("args");
args.setAccessible(true);
Object[] parameters = (Object[]) args.get(aps);
log.debug("SQL query: [{}]\tParams: {} ", getSql(psc), Arrays.toString(parameters));
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new GenericException(e.toString(), e);
}
}
}
return super.query(psc, pss, rse);
}
private static String getSql(Object sqlProvider) { // this code is also found in the JDBCTemplate class
if (sqlProvider instanceof SqlProvider) {
return ((SqlProvider) sqlProvider).getSql();
}
else {
return null;
}
}
}
We use Nhibernate 3.3 to connect to our Sybase Ase 15 database. Everything is fine except for the non support of the limit (or top). It is implemented in sybase but not in Nhibernate.
Do you have a solution?
I tried to create a CustomSybaseAse15Dialect where I change this:
public override bool SupportsLimitOffset
{
get { return true; }
}
public override SqlString GetLimitString(SqlString sql, SqlString offset, SqlString limit)
{
int insertionPoint = GetAfterSelectInsertPoint(sql);
if (insertionPoint > 0)
{
SqlStringBuilder limitBuilder = new SqlStringBuilder();
limitBuilder.Add("select");
if (insertionPoint > 6)
{
limitBuilder.Add(" distinct ");
}
limitBuilder.Add(" top ");
limitBuilder.Add(limit);
if (offset != null)
{
limitBuilder.Add(" start at ");
limitBuilder.Add(offset);
}
limitBuilder.Add(sql.Substring(insertionPoint));
return limitBuilder.ToSqlString();
}
else
{
return sql; // unchanged
}
}
/// <summary>
/// Copied from MsSql2000Dialect.
/// </summary>
private int GetAfterSelectInsertPoint(SqlString sql)
{
if (sql.StartsWithCaseInsensitive("select distinct"))
{
return 15;
}
if (sql.StartsWithCaseInsensitive("select"))
{
return 6;
}
throw new NotSupportedException("The query should start with 'SELECT' or 'SELECT DISTINCT'");
}
Using the Linq2Nhibernate syntax, it works good with
Session.Query<product>().First()
limit is correctly set to 1 but if I do this
Session.Query<product>().Take(3).ToList()
limit is set to "?".
What can I do?
as mentioned in the previous comment there is a bug in nHibernate. It is already fixed but not yet included in an official version.
https://nhibernate.jira.com/browse/NH-3281
You can download the main source and build the dll manually from https://github.com/nhibernate/nhibernate-core .
Michael
For anyone finding this question recently:
This is fixed in the release version of nHibernate 4.1.
You also need to add to the dialect:
public override bool SupportsVariableLimit { get { return false; } }
to address the lack of support for placeholders in "select top X" (it defaults to whatever SupportsLimit is)
I am trying to create an NHibernate IUserType for the Noda Time LocalTime type which would logically map to a time type in Sql Server 2008/2012. I am able to get values saving and loading from the database. However, I can't write queries involving comparison of local times like _session.Query<SchedulingTemplate>().Where(x => x.Start < end && x.End >= start) gives the error SqlException (0x80131904): The data types time and datetime are incompatible in the less than operator.
The relevant code from my user type is:
public Type ReturnedType
{
get { return typeof(LocalTime); }
}
public override object NullSafeGet(IDataReader rs, string[] names, object owner)
{
var dbValue = NHibernateUtil.Time.NullSafeGet(rs, names);
if(dbValue == null)
return null;
return LocalDateTime.FromDateTime((DateTime)dbValue).TimeOfDay;
}
public override void NullSafeSet(IDbCommand cmd, object value, int index)
{
if(value == null)
NHibernateUtil.Time.NullSafeSet(cmd, null, index);
else
NHibernateUtil.Time.NullSafeSet(cmd, ((LocalTime)value).LocalDateTime.ToDateTimeUnspecified(), index);
}
public override SqlType[] SqlTypes
{
get { return new[] { SqlTypeFactory.Time }; }
}
The problem is that despite the above code indicating the database type is a time, it generates the following query (per Sql Profiler):
exec sp_executesql N'select [...] from [SchedulingTemplate] scheduling0_ where scheduling0_.Start<#p0 and scheduling0_.[End]>=#p1',N'#p0 datetime,#p1 datetime',#p0='1753-01-01 20:00:00',#p1='1753-01-01 06:00:00'
(note I omitted the select list for brevity)
Notice that the type and value of the parameters is being treated as datetime.
This appears to be very similar to two NH bugs that have been closed https://nhibernate.jira.com/browse/NH-2661 and https://nhibernate.jira.com/browse/NH-2660.
I tried to use NHibernateUtil.TimeAsTimeSpan and that didn't seem to work either. It generated exactly the same query which surprised me. I am thinking maybe the issue described in NH-2661 also exists for user types and was not fixed for that?
I am using NHibernate v3.3.1.400 and Noda Time 1.0.0-beta2
Following #Firo's advice, I worked from the time SqlType and came up with this:
using NHibernate;
using NHibernate.Dialect;
using NHibernate.SqlTypes;
using NHibernate.Type;
using NodaTime;
using NodaTime.Text;
using System;
using System.Data;
using System.Data.SqlClient;
[Serializable]
public class LocalTimeType : PrimitiveType, IIdentifierType
{
private readonly LocalTimePattern _timePattern = LocalTimePattern.CreateWithInvariantCulture("h:mm:ss tt");
public LocalTimeType() : base(SqlTypeFactory.Time) { }
public override string Name
{
get { return "LocalTime"; }
}
public override object Get(IDataReader rs, int index)
{
try
{
if (rs[index] is TimeSpan) //For those dialects where DbType.Time means TimeSpan.
{
var time = (TimeSpan)rs[index];
return LocalTime.Midnight + Period.FromTicks(time.Ticks);
}
var dbValue = Convert.ToDateTime(rs[index]);
return LocalDateTime.FromDateTime(dbValue).TimeOfDay;
}
catch (Exception ex)
{
throw new FormatException(string.Format("Input string '{0}' was not in the correct format.", rs[index]), ex);
}
}
public override object Get(IDataReader rs, string name)
{
return Get(rs, rs.GetOrdinal(name));
}
public override Type ReturnedClass
{
get { return typeof(LocalTime); }
}
public override void Set(IDbCommand st, object value, int index)
{
var parameter = ((SqlParameter)st.Parameters[index]);
parameter.SqlDbType = SqlDbType.Time; // HACK work around bad behavior, M$ says not ideal, but as intended, NH says this is a bug in MS may work around eventually
parameter.Value = new TimeSpan(((LocalTime)value).TickOfDay);
}
public override bool IsEqual(object x, object y)
{
return Equals(x, y);
}
public override int GetHashCode(object x, EntityMode entityMode)
{
return x.GetHashCode();
}
public override string ToString(object val)
{
return _timePattern.Format((LocalTime)val);
}
public object StringToObject(string xml)
{
return string.IsNullOrEmpty(xml) ? null : FromStringValue(xml);
}
public override object FromStringValue(string xml)
{
return _timePattern.Parse(xml).Value;
}
public override Type PrimitiveClass
{
get { return typeof(LocalTime); }
}
public override object DefaultValue
{
get { return new LocalTime(); }
}
public override string ObjectToSQLString(object value, Dialect dialect)
{
return "'" + _timePattern.Format((LocalTime)value) + "'";
}
}
The key code is in the Set method where is says:
var parameter = ((SqlParameter)st.Parameters[index]);
parameter.SqlDbType = SqlDbType.Time;
This is needed because the MS data provider takes setting the DbType to DbType.Time to mean the underlying type should be DateTime. You must set the SqlDbType to time for it to work.
I am having the difficulty to understand NHibernate an petapoco loading mechanism. Actually I did a test to compare how both behave upon a query.
My class is as follows:
UserTest.cs with the following properties:
private string name;
private int id;
private int customerId;
public int ID
{
get { return id; }
set { id = value; }
}
public string Name
{
get { return name; }
set { name = value; }
}
public int? CustomerID
{
get { return customerId; }
set
{
if (value != customerId)
{
customerId = value;
if (this.ID > 0)
{
DoSomeOtherWork();
}
}
}
}
When I do a User.Load in NHibernate, I have observed that DoSomeOtherWork is never called whereas in PetaPoco, when I do a query from loading User such as Connection.db.Fetch<UserTest>(...) or Connection.db.Query<UserTest>(...), I can see that DoSomeOtherWork is called.
Why is that so?
Is there a way to avoid calling DoSomeOherWork when using PetaPoco such that it has the same behaviour as NHibernate? I dont want to usePetaPoco.Ignoreas I need to get and set theCustomerID`.
PetaPoco it a micro-ORM (much lighter than Nhibernate) and materializes your POCO object when you fetch the record. There is no other magic than that, so the answer is:
No, you can't avoid calling the setter of the property.
I built a custom collector for Lucene.Net, but I can't figure out how to order (or page) the results. Everytime Collect gets called, I can add the result to an internal PriorityQueue, which I understand is the correct way to do this.
I extended the PriorityQueue, but it requires a size parameter on creation. You have to call Initialize in the constructor and pass in the max size.
However, in a collector, the searcher just calls Collect when it gets a new result, so I don't know how many results I have when I create the PriorityQueue. Based on this, I can't figure out how to make the PriorityQueue work.
I realize I'm probably missing something simple here...
PriorityQueue is not SortedList or SortedDictionary.
It is a kind of sorting implementation where it returns the top M results(your PriorityQueue's size) of N elements. You can add with InsertWithOverflow as many items as you want, but it will only hold only the top M elements.
Suppose your search resulted in 1000000 hits. Would you return all of the results to user?
A better way would be to return the top 10 elements to the user(using PriorityQueue(10)) and
if the user requests for the next 10 result, you can make a new search with PriorityQueue(20) and return the next 10 elements and so on.
This is the trick most search engines like google uses.
Everytime Commit gets called, I can add the result to an internal PriorityQueue.
I can not undestand the relationship between Commit and search, Therefore I will append a sample usage of PriorityQueue:
public class CustomQueue : Lucene.Net.Util.PriorityQueue<Document>
{
public CustomQueue(int maxSize): base()
{
Initialize(maxSize);
}
public override bool LessThan(Document a, Document b)
{
//a.GetField("field1")
//b.GetField("field2");
return //compare a & b
}
}
public class MyCollector : Lucene.Net.Search.Collector
{
CustomQueue _queue = null;
IndexReader _currentReader;
public MyCollector(int maxSize)
{
_queue = new CustomQueue(maxSize);
}
public override bool AcceptsDocsOutOfOrder()
{
return true;
}
public override void Collect(int doc)
{
_queue.InsertWithOverflow(_currentReader.Document(doc));
}
public override void SetNextReader(IndexReader reader, int docBase)
{
_currentReader = reader;
}
public override void SetScorer(Scorer scorer)
{
}
}
searcher.Search(query,new MyCollector(10)) //First page.
searcher.Search(query,new MyCollector(20)) //2nd page.
searcher.Search(query,new MyCollector(30)) //3rd page.
EDIT for #nokturnal
public class MyPriorityQueue<TObj, TComp> : Lucene.Net.Util.PriorityQueue<TObj>
where TComp : IComparable<TComp>
{
Func<TObj, TComp> _KeySelector;
public MyPriorityQueue(int size, Func<TObj, TComp> keySelector) : base()
{
_KeySelector = keySelector;
Initialize(size);
}
public override bool LessThan(TObj a, TObj b)
{
return _KeySelector(a).CompareTo(_KeySelector(b)) < 0;
}
public IEnumerable<TObj> Items
{
get
{
int size = Size();
for (int i = 0; i < size; i++)
yield return Pop();
}
}
}
var pq = new MyPriorityQueue<Document, string>(3, doc => doc.GetField("SomeField").StringValue);
foreach (var item in pq.Items)
{
}
The reason Lucene's Priority Queue is size limited is because it uses a fixed size implementation that is very fast.
Think about what is the reasonable maximum number of results to get back at a time and use that number, the "waste" for when the results are few is not that bad for the benefit it gains.
On the other hand, if you have such a huge number of results that you cannot hold them, then how are you going to be serving/displaying them? Keep in mind that this is for "top" hits so as you iterate through the results you will be hitting less and less relevant ones anyway.