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  • Oracle performance problem

    - by jreid42
    We are using an Oracle 11G machine that is very powerful; has redundant storage etc. It's a beast from what I have been told. We just got this DB for a tool that when I first came on as a coop had like 20 people using, now its upwards of 150 people. I am the only one working on it :( We currently have a system in place that distributes PERL scripts across our entire data center essentially giving us a sort of "grid" computing power. The Perl scripts run a sort of simulation and report back the results to the database. They do selects / inserts. The load is not very high for each script but it could be happening across 20-50 systems at the same time. We then have multiple data centers and users all hitting the same database with this same approach. Our main problem with this is that our database is getting overloaded with connections and having to drop some. We sometimes have upwards of 500 connections. These are old perl scripts and they do not handle this well. Essentially they fail and the results are lost. I would rather avoid having to rewrite a lot of these as they are poorly written, and are a headache to even look at. The database itself is not overloaded, just the connection overhead is too high. We open a connection, make a quick query and then drop the connection. Very short connections but many of them. The database team has basically said we need to lower the number of connections or they are going to ignore us. Because this is distributed across our farm we cant implement persistent connections. I do this with our webserver; but its on a fixed system. The other ones are perl scripts that get opened and closed by the distribution tool and thus arent always running. What would be my best approach to resolving this issue? The scripts themselves can wait for a connection to be open. They do not need to act immediately. Some sort of queing system? I've been suggested to set up a few instances of a tool called "SQL Relay". Maybe one in each data center. How reliable is this tool? How good is this approach? Would it work for what we need? We could have one for each data center and relay requests through it to our main database, keeping a pipeline of open persistent connections? Does this make sense? Is there any other suggestions you can make? Any ideas? Any help would be greatly appreciated. Sadly I am just a coop student working for a very big company and somehow all of this has landed all on my shoulders (there is literally nobody to ask for help; its a hardware company, everybody is hardware engineers, and the database team is useless and in India) and I am quite lost as what the best approach would be? I am extremely overworked and this problem is interfering with on going progress and basically needs to be resolved as quickly as possible; preferably without rewriting the whole system, purchasing hardware (not gonna happen), or shooting myself in the foot. HELP LOL!

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  • ORA-12514 TNS:listener does not currently know of service requested in connect descriptor

    - by Jacques
    We have an application running locally which two days worked fine and now we get the: TNS:listener does not currently know of service requested in connect descriptor error. I've tested the connection using TNSPing which resolved correctly and Tried SQLPlus to try connecting, which failed with the same error. (i.e. Sqlplus username/passowrd@addressname[or host name] The TNS Listener on the server is running. Oracle itself on the server is running. We don't know of any changes that were made to this environment. Anything else we can test to figure this one out? Thanks, Jacques

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  • Avoid implicit conversion from date to timestamp for selects with Oracle 11g using Hibernate

    - by sapporo
    I'm using Hibernate 3.2.1 criteria queries to select rows from an Oracle 11g database, filtering by a timestamp field. The field in question is of type java.util.Date in Java, and DATE in Oracle. It turns out that the field gets mapped to java.sql.Timestamp, and Oracle converts all rows to TIMESTAMP before comparing to the passed in value, bypassing the index and thereby ruining performance. One solution would be to use Hibernate's sqlRestriction() along with Oracle's TO_DATE function. That would fix performance, but requires rewriting the application code (lots of queries). So is there a more elegant solution? Since Hibernate already does type mapping, could it be configured to do the right thing?

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  • Sleep function in ORACLE

    - by Salvador
    I need execute an sql query in ORACLE it takes a certain amount of time. so i wrote this function CREATE OR REPLACE FUNCTION MYSCHEMA.TEST_SLEEP ( TIME_ IN NUMBER ) RETURN INTEGER IS BEGIN DBMS_LOCK.sleep(seconds => TIME_); RETURN 1; EXCEPTION WHEN OTHERS THEN RAISE; RETURN 1; END TEST_SLEEP; and i call in this way SELECT TEST_SLEEP(10.5) FROM DUAL but to work i need set grant of DBMS_LOCK to the owner of the procedure. how i can rewrite this function without using the DBMS_LOCK.sleep function? Thanks in advance.

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  • Oracle 11g connection prob.

    - by Kuldeep dwivedi
    Our application is based on Oracle 11g database its drivers already installed but application throws an error on runtime. "AppliMSP.ADOcommands.GetConnected Error while connecting, Provider cannot be found, It may not be properly installed." I am using OraOLEDB.oracle provider. This provider work properly on other module (Administration) of this application but as I want to connect as client with same name and password I get above error. I have tried with MSDAORA(Oracle) but I don't get any success. Can anyone help me?

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  • Improving Performance of Crystal Reports using Stored Procedures

    - by mjh41
    Recently I updated a Crystal Report that was doing all of its work on the client-side (Selects, formulas, etc) and changed all of the logic to be done on the server-side through Stored Procedures using an Oracle 11g database. Now the report is only being used to display the output of the stored procedures and nothing else. Everything I have read on this subject says that utilizing stored procedures should greatly reduce the running time of the report, but it still takes roughly the same amount of time to retrieve the data from the server. Is there something wrong with the stored procedure I have written, or is the issue in the Crystal Report itself? Here is the stored procedure code along with the package that defines the necessary REF CURSOR. CREATE OR REPLACE PROCEDURE SP90_INVENTORYDATA_ALL ( invdata_cur IN OUT sftnecm.inv_data_all_pkg.inv_data_all_type, dCurrentEndDate IN vw_METADATA.CASEENTRCVDDATE%type, dCurrentStartDate IN vw_METADATA.CASEENTRCVDDATE%type ) AS BEGIN OPEN invdata_cur FOR SELECT vw_METADATA.CREATIONTIME, vw_METADATA.RESRESOLUTIONDATE, vw_METADATA.CASEENTRCVDDATE, vw_METADATA.CASESTATUS, vw_METADATA.CASENUMBER, (CASE WHEN vw_METADATA.CASEENTRCVDDATE < dCurrentStartDate AND ( (vw_METADATA.CASESTATUS is null OR vw_METADATA.CASESTATUS != 'Closed') OR TO_DATE(vw_METADATA.RESRESOLUTIONDATE, 'MM/DD/YYYY') >= dCurrentStartDate) then 1 else 0 end) InventoryBegin, (CASE WHEN (to_date(vw_METADATA.RESRESOLUTIONDATE, 'MM/DD/YYYY') BETWEEN dCurrentStartDate AND dCurrentEndDate) AND vw_METADATA.RESRESOLUTIONDATE is not null AND vw_METADATA.CASESTATUS is not null then 1 else 0 end) CaseClosed, (CASE WHEN vw_METADATA.CASEENTRCVDDATE BETWEEN dCurrentStartDate AND dCurrentEndDate then 1 else 0 end) CaseCreated FROM vw_METADATA WHERE vw_METADATA.CASEENTRCVDDATE <= dCurrentEndDate ORDER BY vw_METADATA.CREATIONTIME, vw_METADATA.CASESTATUS; END SP90_INVENTORYDATA_ALL; And the package: CREATE OR REPLACE PACKAGE inv_data_all_pkg AS TYPE inv_data_all_type IS REF CURSOR RETURN inv_data_all_temp%ROWTYPE; END inv_data_all_pkg;

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  • How to make a GRANT persist for a table that's being dropped and re-created?

    - by Eli Courtwright
    I'm on a fairly new project where we're still modifying the design of our Oracle 11g database tables. As such, we drop and re-create our tables fairly often to make sure that our table creation scripts work as expected whenever we make a change. Our database consists of 2 schemas. One schema has some tables with INSERT triggers which cause the data to sometimes be copied into tables in our second schema. This requires us to log into the database with an admin account such as sysdba and GRANT access to the first schema to the necessary tables on the second schema, e.g. GRANT ALL ON schema_two.SomeTable TO schema_one; Our problem is that every time we make a change to our database design and want to drop and re-create our database tables, the access we GRANT-ed to schema_one went away when the table was dropped. Thus, this creates another annoying step wherein we must log in with an admin account to re-GRANT the access every time one of these tables is dropped and re-created. This isn't a huge deal, but I'd love to eliminate as many steps as possible from our development and testing procedures. Is there any way to GRANT access to a table in such a way that the GRANT-ed permissions survive a table being dropped and then re-created? And if this isn't possible, then is there a better way to go about this?

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  • ORACLE XML publishing

    - by Seedorf
    Hey guys, I was wondering which tool in ORACLE 11g (their latest DBMS) can be used for publishing XML. I am about to download it but would first like to know the name of the XML publisher and where I could get more information about it from. Thanks in advance. S

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  • SQLDeveloper using over 100MB of PGA

    - by Leigh Riffel
    Perhaps this is normal, but in my Oracle 11g database I am seeing programmers using Oracle's SQL Developer regularly consume more than 100MB of combined UGA and PGA memory. I'd like to know if this is normal and what can be done about it. Our database is on the 32 bit version of Windows 2008, so memory limitations are becoming an increasing concern. I am using the following query to show the memory usage: SELECT e.SID, e.username, e.status, b.PGA_MEMORY FROM v$session e LEFT JOIN (select y.SID, y.value pga, TO_CHAR(ROUND(y.value/1024/1024),99999999) || ' MB' PGA_MEMORY from v$sesstat y, v$statname z where y.STATISTIC# = z.STATISTIC# and NAME = 'session pga memory') b ON e.sid=b.sid WHERE (PGA)/1024/1024 > 20 ORDER BY 4 DESC; It seems that the resource usage goes up any time a table is opened in SQLDeveloper, but even when it is closed the memory does not go away. The problem is worse if the table is sorted while it was open as that seems to use even more memory. I understand how this would use memory while it is sorting, and perhaps even while it is still open, but to use memory after it is closed seems wrong to me. Can anyone confirm this? Update: I discovered that my numbers were off due to not understanding that the UGA is stored in the PGA under dedicated server mode. This makes the numbers lower than they were, but the problem still remains that SQL Developer seems to use excessive PGA.

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  • Oracle Data Provider and casting

    - by mrjoltcola
    I use Oracle's specific data provider, not the Microsoft provider that is being discontinued. The thing I've found about ODP.NET is how picky it is with data types. Where JDBC and other ADO providers just convert and make things work, ODP.NET will throw an invalid cast exception unless you get it exactly right. Consider this code: String strSQL = "SELECT DOCUMENT_SEQ.NEXTVAL FROM DUAL"; OracleCommand cmd = new OracleCommand(strSQL, conn); reader = cmd.ExecuteReader(); if (reader != null && reader.Read()) { Int64 id = reader.GetInt64(0); return id; } Due to ODP.NET's pickiness on conversion, this doesn't work. My usual options are: 1) Retrieve into a Decimal and return it with a cast to an Int64 (I don't like this because Decimal is just overkill, and at least once I remember reading it was deprecated...) Decimal id = reader.GetDecimal(0); return (Int64)id; 2) Or cast in the SQL statement to make sure it fits into Int64, like NUMBER(18) String strSQL = "SELECT CAST(DOCUMENT_SEQ.NEXTVAL AS NUMBER(18)) FROM DUAL"; I do (2), because I feel its just not clean pulling a number into a .NET Decimal when my domain types are Int32 or Int64. Other providers I've used are nice (smart) enough to do the conversion on the fly. Any suggestions from the ODP.NET gurus?

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  • Accessing the Custom Object Return type from ojdbc6 JDBC Thin Drivers

    - by Andrew Harmel-Law
    I'm writing some JDBC code which calls a Oracle 11g PL/SQL procdedure which has a Custom Object return type. I can get the code to call the procedure, but how do I access the returned Custom Object to obtain it's contained values?. An example of my code calling the procedure is below: PLSQL Code: Procedure GetDataSummary (p_my_key IN KEYS.MY_KEY%TYPE, p_recordset OUT data_summary_tab, p_status OUT VARCHAR2); Java Code: String query = "begin manageroleviewdata.getdatasummary(?, ?, ?); end;"); CallableStatement stmt = conn.prepareCall(query); stmt.setInt(1, 83); stmt.registerOutParameter(2, OracleTypes.ARRAY, "DATA_SUMMARY_TAB"); stmt.registerOutParameter(3, OracleTypes.VARCHAR); stmt.execute(stmt); How do I get the result back fron this?

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  • cx_Oracle makes subprocess give OSError

    - by Shrikant Sharat
    I am trying to use the cx_Oracle module with python 2.6.6 on ubuntu Maverick, with Oracle 11gR2 Enterprise edition. I am able to connect to my oracle db just fine, but once I do that, the subprocess module does not work anymore. Here is an iPython session that reproduces the problem... In [1]: import subprocess as sp, cx_Oracle as dbh In [2]: sp.call(['whoami']) sharat Out[2]: 0 In [3]: con = dbh.connect('system', 'password') In [4]: con.close() In [5]: sp.call(['whomai']) --------------------------------------------------------------------------- OSError Traceback (most recent call last) /home/sharat/desk/calypso-launcher/<ipython console> in <module>() /usr/lib/python2.6/subprocess.pyc in call(*popenargs, **kwargs) 468 retcode = call(["ls", "-l"]) 469 """ --> 470 return Popen(*popenargs, **kwargs).wait() 471 472 /usr/lib/python2.6/subprocess.pyc in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags) 621 p2cread, p2cwrite, 622 c2pread, c2pwrite, --> 623 errread, errwrite) 624 625 if mswindows: /usr/lib/python2.6/subprocess.pyc in _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite) 1134 1135 if data != "": -> 1136 _eintr_retry_call(os.waitpid, self.pid, 0) 1137 child_exception = pickle.loads(data) 1138 for fd in (p2cwrite, c2pread, errread): /usr/lib/python2.6/subprocess.pyc in _eintr_retry_call(func, *args) 453 while True: 454 try: --> 455 return func(*args) 456 except OSError, e: 457 if e.errno == errno.EINTR: OSError: [Errno 10] No child processes So, the call to sp.call works fine before connecting to oracle, but breaks after that. Even if I have closed the connection to the database. Looking around, I found http://bugs.python.org/issue1731717 as somewhat related to this issue, but I am not dealing with threads here. I don't know if cx_Oracle is. Moreover, the above issue mentions that adding a time.sleep(1) fixes it, but it didn't help me. Any help appreciated. Thanks.

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  • Listener error not connecting

    - by Sham
    I have two database running on Port No : 1521. When i m connecting to ORCL db it get's connected, but when i try to connect to another DB it gives me following error. ORA-12514: TNS:listener does not currently know of service requested in connect descriptor. My Listener: # listener.ora Network Configuration File: C:\app\Administrator\product\11.2.0 \dbhome_1\network\admin\listener.ora # Generated by Oracle configuration tools. ADMIN_RESTRICTIONS_LISTENER = ON LISTENER = (DESCRIPTION_LIST = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 127.1.1.1)(PORT = 1521)) ) ) ADR_BASE_LISTENER = C:\app\Administrator TNSNAMES.ora ORCL = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = 127.1.1.1)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orcl) ) ) PARIVARTAN = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 127.1.1.1)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = Parivartan) ) ) Lsnrctl Result STATUS of the LISTENER ------------------------ Alias LISTENER Version TNSLSNR for 64-bit Windows: Version 11.2.0.1.0 - Production Start Date 14-DEC-2012 14:22:51 Uptime 0 days 0 hr. 19 min. 31 sec Trace Level off Security ON: Local OS Authentication SNMP OFF Listener Parameter File C:\app\Administrator\product\11.2.0\dbhome_1\network\a dmin\listener.ora Listener Log File c:\app\administrator\diag\tnslsnr\127.1.1.1\listener\al ert\log.xml Listening Endpoints Summary... (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=127.1.1.1)(PORT=1521))) Services Summary... Service "orcl" has 1 instance(s). Instance "orcl", status READY, has 1 handler(s) for this service... Service "orclXDB" has 1 instance(s). Instance "orcl", status READY, has 1 handler(s) for this service... The command completed successfully Reply me soon....

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  • Calling an Oracle PL/SQL procedure with Custom Object return types from 0jdbc6 JDBCthin drivers

    - by Andrew Harmel-Law
    I'm writing some JDBC code which calls a Oracle 11g PL/SQL procdedure which has a Custom Object return type. Whenever I try an register my return types, I get either ORA-03115 or PLS-00306 as an error when the statement is executed depending on the type I set. An example is below: PLSQL Code: Procedure GetDataSummary (p_my_key IN KEYS.MY_KEY%TYPE, p_recordset OUT data_summary_tab, p_status OUT VARCHAR2); Java Code: String query = "beginmanageroleviewdata.getdatasummary(?, ?, ?); end;"); CallableStatement stmt = conn.prepareCall(query); stmt.setInt(1, 83); stmt.registerOutParameter(2, OracleTypes.CURSOR); // Causes error: PLS-00306 stmt.registerOutParameter(3, OracleTypes.VARCHAR); stmt.execute(stmt); // Error mentioned above thrown here. Can anyone provide me with an example showing how I can do this? I guess it's possible. However I can't see a rowset OracleType. CURSOR, REF, DATALINK, and more fail. Apologies if this is a dumb question. I'm not a PL/SQL expert and may have used the wrong terminology in some areas of my question. (If so, please edit me). Thanks in advance. Regs, Andrew

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  • Oracle Schema Design: Seperate Schema with I/O Overhead?

    - by Guru
    We are designing database schema for a new system based on Oracle 11gR1. We have identified a main schema which would have close to 100 tables, these will be accessed from the front end Java application. We have a requirement to audit the values which got changed in close to 50 tables, this has to be done every row. Which means, it is possible that, for a single row in MYSYS.T1 there might be 50 (or more) rows in MYSYS_AUDIT.T1_AUD table. We might be having old values of every column entry and new values available from T1. DBA gave an observation, advising against this method, because he said, separate schema meant an extra I/O for every operation. Basically AUDIT schema would be used only to do some analyse and enter values (thus SELECT and INSERT). Is it true that, "a separate schema means an extra I/O" ? I could not find justification. It appears logical to me, as the AUDIT data should not be tampered with, so a separate schema. Also, we designed a separate schema for archiving some tables from MYSYS. From MYSYS_ARC the table might be backed up into tapes or deleted after sufficient time. Few stats: Few tables (close to 20, 30) in MYSYS schema could grow to around 50M rows. We have asked for a total disk space of 4 TB. MYSYS_AUDIT schema might be having 10 times that of MYSYS but we wont keep them more than 3 months. Questions Given all these, can you suggest me any improvements? Separate schema affects disc I/O? (one extra I/O for every schema ?) Any general suggestions? Figure: +-------------------+ +-------------------+ | MYSYS | | MYSYS_AUDIT | | | | | | 1. T1 | | 1. T1_AUD | | 2. T2 | | 2. T2_AUD | | 3. T3 |--------->| 3. T3_AUD | | 4. T4 |(SELECT, | 4. T4_AUD | | . | INSERT) | . | | . | | . | | . | | . | | 100. T100 | | 50. T50_AUD | +-------------------+ +-------------------+ | | | | |(INSERT) | | | * +-------------------+ | MYSYS_ARC | | | | 1. T1_ARC | | 2. T2_ARC | | 3. T3_ARC | | 4. T4_ARC | | . | | . | | . | | 100. T100_ARC | +-------------------+ Apart from this, we have two more schemas with only read only rights, but mainly they are for adhoc purpose and we dont mind the performance on them.

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  • SharePoint Visual web part and Oracle connection problem

    - by Rishi
    Hi, I'm trying to build a "visual web part" for SharePoint 2010 which should connect to Oracle table and display records on SharePoint page.For development, Oracle 11g client (with ODP.net) ,SharePoint server 2010, Visual Studio 2010 and Oracle 10g express all running on my machine. First,I've written sample code in ASP.NET web app to connect my local Oracle table and display data in grid view and it works fine. My code is , OracleConnection con; try { // Connect string constr = "Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=XE)));User Id=SYSTEM; Password=password"; con = new OracleConnection(constr); //Open database connection con.Open(); // Execute a SQL SELECT OracleCommand cmd = new OracleCommand("select * from T_ACTIONPOINTS WHERE AP_STATUS='Active' ", con); OracleDataReader dr = cmd.ExecuteReader(); GridView.DataSource = dr; GridView.DataBind(); GridView.AllowPaging = true; } catch (Exception e) { lblError.Text = e.Message; } Now, I'm trying to create new "SharePoint" visual web part project and using same code and deploying it on my local SP server. But when it runs , I get following error here is my solution explorer, It looks something wrong in compatibility.Can someone point me in right direction ?

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  • BigDecimal precision not persisted with javax.persistence annotations

    - by dkaczynski
    I am using the javax.persistence API and Hibernate to create annotations and persist entities and their attributes in an Oracle 11g Express database. I have the following attribute in an entity: @Column(precision = 12, scale = 9) private BigDecimal weightedScore; The goal is to persist a decimal value with a maximum of 12 digits and a maximum of 9 of those digits to the right of the decimal place. After calculating the weightedScore, the result is 0.1234, but once I commit the entity with the Oracle database, the value displays as 0.12. I can see this by either by using an EntityManager object to query the entry or by viewing it directly in the Oracle Application Express (Apex) interface in a web browser. How should I annotate my BigDecimal attribute so that the precision is persisted correctly? Note: We use an in-memory HSQL database to run our unit tests, and it does not experience the issue with the lack of precision, with or without the @Column annotation.

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  • Oracle Merge Rejection Row Count

    - by Andrew
    Given an Oracle Merge statement with a rejection limit, is there a shorthand way to identify how many rows were rejected, without being forced to query the rejection destination? The rejection destination has records pre-merge, so would currently have to be counted twice and the difference taken, but it seems like there should be a counter exposed, given that it has to be aware of whether it has exceeded the rejection limit.

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  • Oracle Hash Cluster Overflow Blocks

    - by Andrew
    When inserting a large number of rows into a single table hash cluster in Oracle, it will fill up the block with any values that hash to that hash-value and then start using overflow blocks. These overflow blocks are listed as chained off the main block, but I can not find detailed information on the way in which they are allocated or chained. When an overflow block is allocated for a hash value, is that block exclusively allocated to that hash value, or are the overflow blocks used as a pool and different hash values can then start using the same overflow block. How is the free space of the chain monitored - in that, as data is continued to be inserted, does it have to traverse the entire chain to find out if it has some free space in the current overflow chain, and then if it finds none, it then chooses to allocate a new block?

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  • Revert scan state when prompting for variable values

    - by Dave Jarvis
    How do you detect the current SCAN state and revert it after changing it? An exerpt from the script in question: SET SCAN OFF SET ECHO ON SET SQLBLANKLINES ON SET SCAN ON UPDATE TABLE_NAME SET CREATED_BY = &&created_by; SET SCAN OFF The problem is that if the script doesn't have the first line (SET SCAN OFF), then the code to prompt the user should not turn the SCAN state off. In pseudocode, we'd like to do the following: SET SCAN OFF SET ECHO ON SET SQLBLANKLINES ON PUSH SCAN STATE SET SCAN ON UPDATE TABLE_NAME SET CREATED_BY = &&created_by; POP SCAN STATE The psudeocode PUSH SCAN STATE remembers the state so that if the code is altered by removing the first line, the rest of the script still works as expected.

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  • NHibernate (3.1.0.4000) NullReferenceException using Query<> and NHibernate Facility

    - by TigerShark
    I have a problem with NHibernate, I can't seem to find any solution for. In my project I have a simple entity (Batch), but whenever I try and run the following test, I get an exception. I've triede a couple of different ways to perform a similar query, but almost identical exception for all (it differs in which LINQ method being executed). The first test: [Test] public void QueryLatestBatch() { using (var session = SessionManager.OpenSession()) { var batch = session.Query<Batch>() .FirstOrDefault(); Assert.That(batch, Is.Not.Null); } } The exception: System.NullReferenceException : Object reference not set to an instance of an object. at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery) at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) at System.Linq.Queryable.FirstOrDefault(IQueryable`1 source) The second test: [Test] public void QueryLatestBatch2() { using (var session = SessionManager.OpenSession()) { var batch = session.Query<Batch>() .OrderBy(x => x.Executed) .Take(1) .SingleOrDefault(); Assert.That(batch, Is.Not.Null); } } The exception: System.NullReferenceException : Object reference not set to an instance of an object. at NHibernate.Linq.NhQueryProvider.PrepareQuery(Expression expression, ref IQuery query, ref NhLinqExpression nhQuery) at NHibernate.Linq.NhQueryProvider.Execute(Expression expression) at System.Linq.Queryable.SingleOrDefault(IQueryable`1 source) However, this one is passing (using QueryOver<): [Test] public void QueryOverLatestBatch() { using (var session = SessionManager.OpenSession()) { var batch = session.QueryOver<Batch>() .OrderBy(x => x.Executed).Asc .Take(1) .SingleOrDefault(); Assert.That(batch, Is.Not.Null); Assert.That(batch.Executed, Is.LessThan(DateTime.Now)); } } Using the QueryOver< API is not bad at all, but I'm just kind of baffled that the Query< API isn't working, which is kind of sad, since the First() operation is very concise, and our developers really enjoy LINQ. I really hope there is a solution to this, as it seems strange if these methods are failing such a simple test. EDIT I'm using Oracle 11g, my mappings are done with FluentNHibernate registered through Castle Windsor with the NHibernate Facility. As I wrote, the odd thing is that the query works perfectly with the QueryOver< API, but not through LINQ.

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