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  • How to structure the tables of a very simple blog in MySQL?

    - by Programmer
    I want to add a very simple blog feature on one of my existing LAMP sites. It would be tied to a user's existing profile, and they would be able to simply input a title and a body for each post in their blog, and the date would be automatically set upon submission. They would be allowed to edit and delete any blog post and title at any time. The blog would be displayed from most recent to oldest, perhaps 20 posts to a page, with proper pagination above that. Other users would be able to leave comments on each post, which the blog owner would be allowed to delete, but not pre-moderate. That's basically it. Like I said, very simple. How should I structure the MySQL tables for this? I'm assuming that since there will be blog posts and comments, I would need a separate table for each, is that correct? But then what columns would I need in each table, what data structures should I use, and how should I link the two tables together (e.g. any foreign keys)? I could not find any tutorials for something like this, and what I'm looking to do is really offer my users the simplest version of a blog possible. No tags, no moderation, no images, no fancy formatting, etc. Just a simple diary-type, pure-text blog with commenting by other users.

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  • sql statement question. Need to query 3 tables in one go!

    - by Stefan
    Hey there, I have an sql database. In this database is 3 tables I need to query. The first table has all the item info called item and the other two tables has data for votes and comments called userComment and the third for votes called userItem I currently have a function which uses this sql query to get the latest more popular (in terms of both votes and comments): $sql = "SELECT itemID, COUNT(*) AS cnt FROM ( SELECT `itemID` FROM `userItem` WHERE FROM_UNIXTIME( `time` ) >= NOW() - INTERVAL 1 DAY UNION ALL SELECT `itemID` FROM `userComment` WHERE FROM_UNIXTIME( `time` ) >= NOW() - INTERVAL 1 DAY AND `itemID` > 0 ) q GROUP BY `itemID` ORDER BY cnt DESC"; I know how to change this for either by votes alone or comments.... HOWEVER - I need to query the database to only return the itemID's of the ones which have specific conditions in only the item table these are WHERE categoryID = 'xx' AND typeID = 'xx' If the sql ninja could please help me on this one? Do I have to first return the results from the above query and the for each in the array fetched then check each against the item table and see if it fits the conditions to build a new array - or is that overkill? Thanks, Stefan

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  • Can I make an identity field span multiple tables in SQL Server?

    - by johnnycakes
    Can I have an "identity" (unique, non-repeating) column span multiple tables? For example, let's say I have two tables: Books and Authors. Authors AuthorID AuthorName Books BookID BookTitle The BookID column and the AuthorID column are identity columns. I want the identity part to span both columns. So, if there is an AuthorID with a value of 123, then there cannot be a BookID with a value of 123. And vice versa. I hope that makes sense. Is this possible? Thanks. Why do I want to do this? I am writing an APS.NET MVC app. I am creating a comment section. Authors can have comments. Books can have comments. I want to be able to pass an entity ID (a book ID or an author ID) to an action and have the action pull up all the corresponding comments. The action won't care if it's a book or an author or whatever. Sound reasonable?

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  • DB Architecture : Linking to intersection or to main tables?

    - by Jean-Nicolas
    Hi, I'm creating fantasy football system on my website but i'm very confuse about how I should link some of my table. Tables The main table is Pool which have all the info about the ruling of the fantasy draft. A standard table User, which contains the usual stuff. Intersection table called pools_users which contains id,pool_id,user_id because a user could be in more than one pool, and a pool contains more than 1 user. The problem Table Selections = that's the table that is causing problem. That's the selection that the user choose for his pool. This is related to the Player table but thats not relevant for this problem. Should I link this table to the table Pools_users or should I link it with both main table Pool and User. This table contains id,pool_id,user_id,player_id,... What is the best way link my tables? When I want to retrieve my data, I normally want the information to be divided BY users. "This user have those selections, this one those selections, etc).

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  • Sql Server 2005 Database Tables - Row Comparison Column By Column.

    - by Goober
    Scenario I have an TWO datbase tables of exactly the SAME STRUCTURE. The difference between these tables is that one contains data populated by one application and the other is populated by a different application. Each application is trying to produce the same result, but using two different methods of implementation. Proposed Idea What I want to do, is run both applications, which will roughly produce 35000 rows containing 10 columns each - So all in all, 70000 rows of data, I then want to compare each row of data, COLUMN BY COLUMN to check whether the values are the same or not. Current Thoughts Since there is so much data to compare, I feel that the best way in which to do this would be to write an application, preferably in C# (but if necessary, T-sql), to compare each row of data column by column, and write out any failed comparisons to a text log file. Question Could anybody suggest an efficient way in which to perform column by column row comparison for 70000 rows worth of data? I'm struggling for ideas on how to tackle this problem. Extra Detail The two applications are both written in C# .Net 3.5. The Database is running on Sql Server 2005. Help greatly appreciated.

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  • How to join multiple tables using LINQ-to-SQL?

    - by user603245
    Hi! I'm quite new to linq, so please bear with me. I'm working on a asp.net webpage and I want to add a "search function" (textbox where user inputs name or surname or both or just parts of it and gets back all related information). I have two tables ("Person" and "Application") and I want to display some columns from Person (name and surname) and some from Application (score, position,...). I know how I could do it using sql, but I want to learn more about linq and thus I want to do it using linq. For now I got two main ideas: 1.) var person = dataContext.GetTable<Person>(); var application = dataContext.GetTable<Application>(); var p1 = from p in Person where(p.Name.Contains(tokens[0]) || p.Surname.Contains(tokens[1])) select new {Id = p.Id, Name = p.Name, Surname = p.Surname}; //or maybe without this line //I don't know how to do the following properly var result = from a in Application where a.FK_Application.Equals(index) //just to get the "right" type of application //this is not right, but I don't know how to do it better join p1 on p1.Id == a.FK_Person 2.) The other idea is just to go through "Application" and instead of "join p1 ..." to use var result = from a in Application where a.FK_Application.Equals(index) //just to get the "right" type of application join p from Person on p.Id == a.FK_Person where p.Name.Contains(tokens[0]) || p.Surname.Contains(tokens[1]) I think that first idea is better for queries without the first "where" condition, which I also intended to use. Regardless of what is better (faster), I still don't know how to do it using linq. Also in the end I wanted to display / select just some parts (columns) of the result (joined tables + filtering conditions). I really want to know how to do such things using linq as I'll be dealing also with some similar problems with local data, where I can use only linq. Could somebody please explain me how to do it, I spent days trying to figure it out and searching on the internet for answers. Thank you for your time.

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  • How to remove empty tables from a MySQL backup file.

    - by user280708
    I have multiple large MySQL backup files all from different DBs and having different schemas. I want to load the backups into our EDW but I don't want to load the empty tables. Right now I'm cutting out the empty tables using AWK on the backup files, but I'm wondering if there's a better way to do this. If anyone is interested, this is my AWK script: EDIT: I noticed today that this script has some problems, please beware if you want to actually try to use it. Your output may be WRONG... I will post my changes as I make them. # File: remove_empty_tables.awk # Copyright (c) Northwestern University, 2010 # http://edw.northwestern.edu /^--$/ { i = 0; line[++i] = $0; getline if ($0 ~ /-- Definition/) { inserts = 0; while ($0 !~ / ALTER TABLE .* ENABLE KEYS /) { # If we already have an insert: if (inserts > 0) print else { # If we found an INSERT statement, the table is NOT empty: if ($0 ~ /^INSERT /) { ++inserts # Dump the lines before the INSERT and then the INSERT: for (j = 1; j <= i; ++j) print line[j] i = 0 print $0 } # Otherwise we may yet find an insert, so save the line: else line[++i] = $0 } getline # go to the next line } line[++i] = $0; getline line[++i] = $0; getline if (inserts > 0) { for (j = 1; j <= i; ++j) print line[j] print $0 } next } else { print "--" } } { print }

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  • Creating a join based on data from other tables...

    - by Workshop Alex
    I'm dealing with a database structure that can be defined as "illogical". It has about 100 different schema's with all different table structures per schema. Only one common factor is a "Version" table in each schema containing about 4 fields. (Thus, there are about 100 Version tables in the database.) There's also another table (view, actually) containing a list of all the schema's in the database that have a version table. I need a stored procedure that walks through all the schema's and selects all data from the Version table, adding the schema name as a fifth field to the result. Basically, this stored procedure is to return a list of all version records per schema. My idea: first walk through the schema list to create one new SQL statements that will JOIN all the schema.version tables into one SQL statement. Then I return the result of that query. How to do this? Or does anyone have a better suggestion? (No, redesigning the structure is NOT an option.)

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  • [Rails3] How to do multiple many to many relationships between the same two tables.

    - by Kurt
    Hi. I have a model of a club where I want to model the two entities Meeting and Member. There are actually two many-to-many relationships between these entities though, as for any meeting a Member can either be a Speaker or a Guest. Now I am an OO thinker, so would normally just create the two classes and each one would just have two arrays of the other inside, but rails is making me think a bit more data centric here, so I realise I need to break these M2M relationships up with join tables Speakers and Guests which I have done, but now I am having trouble describing the relationships in the models. The two join table models both have "belongs_to :meeting" and "belongs_to :member" and I think that should be sufficient. I am not however sure about the Meeting and Member models though. Each one has "has_many :guests" and "has_many: speakers" but I am not sure if I also want to go: has_many :members, :through = :guests has_many :members, :through = :speakers But I suspect that this is like declaring two "members" that will clash. I also thought about: has_many :guests, :through = :guests has_many :speakers, :through = :speakers Does that make sense? How would ActiveRecord know that they are in fact Members? I have found heaps of examples of polymorphic m2m relationships and m2m relationships where 1 table references itself, but no good examples to help me mode this situation where two separate tables have two different m2m relationships. Anyone got any tips?

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  • Bridge or Factory and How

    - by Chris
    I'm trying to learn patterns and I've got a job that is screaming for a pattern, I just know it but I can't figure it out. I know the filter type is something that can be abstracted and possibly bridged. I'M NOT LOOKING FOR A CODE REWRITE JUST SUGGESTIONS. I'm not looking for someone to do my job. I would like to know how patterns could be applied to this example. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data; using System.IO; using System.Xml; using System.Text.RegularExpressions; namespace CopyTool { class CopyJob { public enum FilterType { TextFilter, RegExFilter, NoFilter } public FilterType JobFilterType { get; set; } private string _jobName; public string JobName { get { return _jobName; } set { _jobName = value; } } private int currentIndex; public int CurrentIndex { get { return currentIndex; } } private DataSet ds; public int MaxJobs { get { return ds.Tables["Job"].Rows.Count; } } private string _filter; public string Filter { get { return _filter; } set { _filter = value; } } private string _fromFolder; public string FromFolder { get { return _fromFolder; } set { if (Directory.Exists(value)) { _fromFolder = value; } else { throw new DirectoryNotFoundException(String.Format("Folder not found: {0}", value)); } } } private List<string> _toFolders; public List<string> ToFolders { get { return _toFolders; } } public CopyJob() { Initialize(); } private void Initialize() { if (ds == null) { ds = new DataSet(); } ds.ReadXml(Properties.Settings.Default.ConfigLocation); LoadValues(0); } public void Execute() { ExecuteJob(FromFolder, _toFolders, Filter, JobFilterType); } public void ExecuteAll() { string OrigPath; List<string> DestPaths; string FilterText; FilterType FilterWay; foreach (DataRow rw in ds.Tables["Job"].Rows) { OrigPath = rw["FromFolder"].ToString(); FilterText = rw["FilterText"].ToString(); switch (rw["FilterType"].ToString()) { case "TextFilter": FilterWay = FilterType.TextFilter; break; case "RegExFilter": FilterWay = FilterType.RegExFilter; break; default: FilterWay = FilterType.NoFilter; break; } DestPaths = new List<string>(); foreach (DataRow crw in rw.GetChildRows("Job_ToFolder")) { DestPaths.Add(crw["FolderPath"].ToString()); } ExecuteJob(OrigPath, DestPaths, FilterText, FilterWay); } } private void ExecuteJob(string OrigPath, List<string> DestPaths, string FilterText, FilterType FilterWay) { FileInfo[] files; switch (FilterWay) { case FilterType.RegExFilter: files = GetFilesByRegEx(new Regex(FilterText), OrigPath); break; case FilterType.TextFilter: files = GetFilesByFilter(FilterText, OrigPath); break; default: files = new DirectoryInfo(OrigPath).GetFiles(); break; } foreach (string fld in DestPaths) { CopyFiles(files, fld); } } public void MoveToJob(int RecordNumber) { Save(); LoadValues(RecordNumber - 1); } public void AddToFolder(string folderPath) { if (Directory.Exists(folderPath)) { _toFolders.Add(folderPath); } else { throw new DirectoryNotFoundException(String.Format("Folder not found: {0}", folderPath)); } } public void DeleteToFolder(int index) { _toFolders.RemoveAt(index); } public void Save() { DataRow rw = ds.Tables["Job"].Rows[currentIndex]; rw["JobName"] = _jobName; rw["FromFolder"] = _fromFolder; rw["FilterText"] = _filter; switch (JobFilterType) { case FilterType.RegExFilter: rw["FilterType"] = "RegExFilter"; break; case FilterType.TextFilter: rw["FilterType"] = "TextFilter"; break; default: rw["FilterType"] = "NoFilter"; break; } DataRow[] ToFolderRows = ds.Tables["Job"].Rows[currentIndex].GetChildRows("Job_ToFolder"); for (int i = 0; i <= ToFolderRows.GetUpperBound(0); i++) { ToFolderRows[i].Delete(); } foreach (string fld in _toFolders) { DataRow ToFolderRow = ds.Tables["ToFolder"].NewRow(); ToFolderRow["JobId"] = ds.Tables["Job"].Rows[currentIndex]["JobId"]; ToFolderRow["Job_Id"] = ds.Tables["Job"].Rows[currentIndex]["Job_Id"]; ToFolderRow["FolderPath"] = fld; ds.Tables["ToFolder"].Rows.Add(ToFolderRow); } } public void Delete() { ds.Tables["Job"].Rows.RemoveAt(currentIndex); LoadValues(currentIndex++); } public void MoveNext() { Save(); currentIndex++; LoadValues(currentIndex); } public void MovePrevious() { Save(); currentIndex--; LoadValues(currentIndex); } public void MoveFirst() { Save(); LoadValues(0); } public void MoveLast() { Save(); LoadValues(ds.Tables["Job"].Rows.Count - 1); } public void CreateNew() { Save(); int MaxJobId = 0; Int32.TryParse(ds.Tables["Job"].Compute("Max(JobId)", "").ToString(), out MaxJobId); DataRow rw = ds.Tables["Job"].NewRow(); rw["JobId"] = MaxJobId + 1; ds.Tables["Job"].Rows.Add(rw); LoadValues(ds.Tables["Job"].Rows.IndexOf(rw)); } public void Commit() { Save(); ds.WriteXml(Properties.Settings.Default.ConfigLocation); } private void LoadValues(int index) { if (index > ds.Tables["Job"].Rows.Count - 1) { currentIndex = ds.Tables["Job"].Rows.Count - 1; } else if (index < 0) { currentIndex = 0; } else { currentIndex = index; } DataRow rw = ds.Tables["Job"].Rows[currentIndex]; _jobName = rw["JobName"].ToString(); _fromFolder = rw["FromFolder"].ToString(); _filter = rw["FilterText"].ToString(); switch (rw["FilterType"].ToString()) { case "TextFilter": JobFilterType = FilterType.TextFilter; break; case "RegExFilter": JobFilterType = FilterType.RegExFilter; break; default: JobFilterType = FilterType.NoFilter; break; } if (_toFolders == null) _toFolders = new List<string>(); _toFolders.Clear(); foreach (DataRow crw in rw.GetChildRows("Job_ToFolder")) { AddToFolder(crw["FolderPath"].ToString()); } } private static FileInfo[] GetFilesByRegEx(Regex rgx, string locPath) { DirectoryInfo d = new DirectoryInfo(locPath); FileInfo[] fullFileList = d.GetFiles(); List<FileInfo> filteredList = new List<FileInfo>(); foreach (FileInfo fi in fullFileList) { if (rgx.IsMatch(fi.Name)) { filteredList.Add(fi); } } return filteredList.ToArray(); } private static FileInfo[] GetFilesByFilter(string filter, string locPath) { DirectoryInfo d = new DirectoryInfo(locPath); FileInfo[] fi = d.GetFiles(filter); return fi; } private void CopyFiles(FileInfo[] files, string destPath) { foreach (FileInfo fi in files) { bool success = false; int i = 0; string copyToName = fi.Name; string copyToExt = fi.Extension; string copyToNameWithoutExt = Path.GetFileNameWithoutExtension(fi.FullName); while (!success && i < 100) { i++; try { if (File.Exists(Path.Combine(destPath, copyToName))) throw new CopyFileExistsException(); File.Copy(fi.FullName, Path.Combine(destPath, copyToName)); success = true; } catch (CopyFileExistsException ex) { copyToName = String.Format("{0} ({1}){2}", copyToNameWithoutExt, i, copyToExt); } } } } } public class CopyFileExistsException : Exception { public string Message; } }

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  • Building Reducisaurus URLs

    - by Alix Axel
    I'm trying to use Reducisaurus Web Service to minify CSS and Javascript but I've run into a problem... Suppose I've two unminified CSS at: http:/domain.com/dynamic/styles/theme.php?color=red http:/domain.com/dynamic/styles/typography.php?font=Arial According to the docs I should call the web service like this: http:/reducisaurus.appspot.com/css?url=http:/domain.com/dynamic/styles/theme.php?color=red And if I want to minify both CSS files at once: http:/reducisaurus.appspot.com/css?url1=http:/domain.com/dynamic/styles/theme.php?color=red&url2=http:/domain.com/dynamic/styles/theme.php?color=red If I wanted to specify a different number of seconds for the cache (3600 for instance) I would use: http:/reducisaurus.appspot.com/css?url=http:/domain.com/dynamic/styles/theme.php?color=red&expire_urls=3600 And again for both CSS files at once: http:/reducisaurus.appspot.com/css?url1=http:/domain.com/dynamic/styles/theme.php?color=red&url2=http:/domain.com/dynamic/styles/theme.php?color=red&expire_urls=3600 Now my question is, how does Reducisaurus knows how to separate the URLs I want? How does it know that &expire_urls=3600 is not part of my URL? And how does it know that &url2=... is not a GET argument of url1? I'm I doing this right? Do I need to urlencode my URLs? I took a peek into the source code and although my Java is very poor it seems that the methods acquireFromRemoteUrl() and getSortedParameterNames() from the BaseServlet.java file hold the answers to my question - if a GET argument name contains - or _ they should be ignored?! What about multiple &url(n)s?

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  • Python 3, urllib ... Reset Connection Possible?

    - by Rhys
    In the larger scale of my program the goal of the below code is to filter out all dynamic html in a web-page source code code snippet: try: deepreq3 = urllib.request.Request(deepurl3) deepreq3.add_header("User-Agent","etc......") deepdata3 = urllib.request.urlopen(deepurl3).read().decode("utf8", 'ignore') The following code is looped 3 times in order to identify whether the target web-page is Dynamic (source code is changed at intervals) or not. If the page IS dynamic, the above code loops another 15 times and attempts to filter out the dynamic content. QUESTION: While this filtering method works 80% of the time, some pages will reload ALL 15 times and STILL contain dynamic code. HOWEVER. If I manually close down the Python Shell and re-execute my program, the dynamic html that my 'refresh-page method' could not shake off is no longer there ... it's been replaced with new dynamic html that my 'refresh-page method' cannot shake off. So I need to know, what is going on here? How is re-running my program causing the dynamic content of a page to change. AND, is there any way, any 'reset connection' command I can use to recreate this ... without manually restarting my app. Thanks for your response.

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  • PHP Warning: PHP Startup: Unable to load dynamic library php_mysql.dll, Mac 10.6, Apache 2.2, php 5

    - by munchybunch
    I'm trying to use the PHP CLI, and when I enter something like php test.php in the command line it returns: PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/extensions/no-debug-non-zts-20090626/php_mysql.dll' - dlopen(/usr/lib/php/extensions/no-debug-non-zts-20090626/php_mysql.dll, 9): image not found in Unknown on line 0 something test.php contains: <?php echo 'something'; ?> I checked /usr/lib/php/extensions/no-debug-non-zts-20090626/, and as expected the .dll file isn't there. I'm a complete beginner when it comes to this - what is happening, and how can I fix it? A search of my system for "php_msyql.dll" reveals nothing. Does it have to do with how I compiled it? I don't have the original version of php that came with the mac, I think - I may have reinstalled it somewhere along the way. Any help would be appreciated!

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  • Does kern.hz still have any relevance in FreeBSD if "dynamic tick mode" is enabled?

    - by Frerich Raabe
    I'm running a FreeBSD 9.0 setup as a virtual machine in a KVM setup. In previous versions of FreeBSD it was common to force the kern.hz setting to a lower value so that the virtual machine does not keep the host busy because it's handling timer interrupts without having any work to do - the FreeBSD Handbook explains: The most important step is to reduce the kern.hz tunable to reduce the CPU utilization of FreeBSD under the Parallels environment. This is accomplished by adding the following line to /boot/loader.conf: kern.hz=100 Without this setting, an idle FreeBSD Parallels guest OS will use roughly 15% of the CPU of a single processor iMac®. After this change the usage will be closer to a mere 5%. However, in FreeBSD 9, the "dynamic tick mode" (aka "tickless mode") is the default, controlled by the kern.eventtimer.periodic setting which defaults to 0 (read: tickless mode). This makes me wonder - does the tip of lowering kern.hz still have any relevance for making FreeBSD 9 play nicely in a virtual machine setup?

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  • How to create dynamic Scatter Plot/Matrix with labels and categories on both axis in Excel 2010?

    - by user1581900
    Let us consider a following data set: Name | Age | Hair Color ----------------------------- John | Young | Brown Sophie | Old | Blond Adam | Mature| Blond Mark | Teen | Dark Jeremy | Old | Grey Alex | Young | Brown etc... Both Age and Hair Color, can take only defined values(Young/teen/mature/old and Blond/brown/Dark/Grey). Name is the only real variable here. I want to create a Scatter Plot / Matrix that will look something like that: I know that I schould use this tool to add labels to the scatter plot. I also found this youtube video that explains how to display categories on Y-axis Moreover I need the chart to be dynamic as explained in another youtube video. How do I combine all these approaches to get a Scatter Plot with categories as values on both axis?

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  • Recommended Free DNS hosting for my webserve on a dynamic IP? [closed]

    - by JSchwartz
    I have finished a webserver project (for school) and the professor wants to be able to "test it" from home whenever he is free - this means I need to provide his with the URL to my webserver (which is fine). The only issue is that my IP-Address is dynamic (changes almost everyday) and I would rather not have to email him everytime - nor do I want him to try when it isn't working ... So I was looking into alternative solutions like DNS hosting (I hope that is the right terminology), so I could provide something static for him to connect to ... problem is I have never done this before... Are there any recommeneded free ones? Does Google or someone provide something good? I found http://www.no-ip.com/ which seems like it does what I want... Any feedback would be appreciated. Thanks,

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  • How can I use geoalchemy with elixir autoload tables?

    - by Dan Ellis
    I'm using geoalchemy and autoloaded tables, but I'd like to use Elixir, because it has a nicer query syntax. Does anyone know how to get them to work together? I did get it working with this code -- http://pastie.textmate.org/private/y3biyvosuejkrtxbpdv1a -- but that still gives the ugly warning about not recognising the geometry column when the table is reflected. Ideally, what I'd like to do is to get SQLAlchemy's own table reflection to recognise the geometry columns. How would I plumb them together?

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  • What can map database tables like LINQ to SQL did?

    - by trnTash
    A good thing in LINQ to SQL was a fast and reliable way to map database tables and convert them into classes accessible from c# project. However it is no longer recommended to create projects using LINQ to SQL. What is its substitute? What kind of tool should I use in VS 2010 today if I want to have the same functionality as I had with LINQ to SQL?

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  • Different behavior between IE6 and Firefox for HTML Tables?

    - by YogoZuno
    I'm doing the first bit of web-page development I've done in years, in VS2008, using VB.net. I have a fairly simple layout, which is using several nested tables. IE6 displays the layout just fine, but Firefox for some reason shows the whole thing in a small panel at the top of the page, with a scrollbar. Can anyone suggest something basic I am likely missing?

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  • Explicit method tables in C# instead of OO - good? bad?

    - by FunctorSalad
    Hi! I hope the title doesn't sound too subjective; I absolutely do not mean to start a debate on OO in general. I'd merely like to discuss the basic pros and cons for different ways of solving the following sort of problem. Let's take this minimal example: you want to express an abstract datatype T with functions that may take T as input, output, or both: f1 : Takes a T, returns an int f2 : Takes a string, returns a T f3 : Takes a T and a double, returns another T I'd like to avoid downcasting and any other dynamic typing. I'd also like to avoid mutation whenever possible. 1: Abstract-class-based attempt abstract class T { abstract int f1(); // We can't have abstract constructors, so the best we can do, as I see it, is: abstract void f2(string s); // The convention would be that you'd replace calls to the original f2 by invocation of the nullary constructor of the implementing type, followed by invocation of f2. f2 would need to have side-effects to be of any use. // f3 is a problem too: abstract T f3(double d); // This doesn't express that the return value is of the *same* type as the object whose method is invoked; it just expresses that the return value is *some* T. } 2: Parametric polymorphism and an auxilliary class (all implementing classes of TImpl will be singleton classes): abstract class TImpl<T> { abstract int f1(T t); abstract T f2(string s); abstract T f3(T t, double d); } We no longer express that some concrete type actually implements our original spec -- an implementation is simply a type Foo for which we happen to have an instance of TImpl. This doesn't seem to be a problem: If you want a function that works on arbitrary implementations, you just do something like: // Say we want to return a Bar given an arbitrary implementation of our abstract type Bar bar<T>(TImpl<T> ti, T t); At this point, one might as well skip inheritance and singletons altogether and use a 3 First-class function table class /* or struct, even */ TDictT<T> { readonly Func<T,int> f1; readonly Func<string,T> f2; readonly Func<T,double,T> f3; TDict( ... ) { this.f1 = f1; this.f2 = f2; this.f3 = f3; } } Bar bar<T>(TDict<T> td; T t); Though I don't see much practical difference between #2 and #3. Example Implementation class MyT { /* raw data structure goes here; this class needn't have any methods */ } // It doesn't matter where we put the following; could be a static method of MyT, or some static class collecting dictionaries static readonly TDict<MyT> MyTDict = new TDict<MyT>( (t) => /* body of f1 goes here */ , // f2 (s) => /* body of f2 goes here */, // f3 (t,d) => /* body of f3 goes here */ ); Thoughts? #3 is unidiomatic, but it seems rather safe and clean. One question is whether there are any performance concerns with it. I don't usually need dynamic dispatch, and I'd prefer if these function bodies get statically inlined in places where the concrete implementing type is known statically. Is #2 better in that regard?

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  • How can I compare tables in two different databases using SQL?

    - by chama
    I'm trying to compare the schemas of two tables that exist in different databases. So far, I have this query SELECT * FROM sys.columns WHERE object_id = OBJECT_ID('table1') The only thing is that I don't know how to use the sys.columns to reference a database other than the one that the query is connected to. I tried this SELECT * FROM db.sys.columns WHERE object_id = OBJECT_ID('table1') but it didn't find anything. I'm using SQL Server 2005 Any suggestions? thanks!

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