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  • Entity framework and database logic.

    - by Xavier Devian
    Hi all, i have a question that's being around for several years. As all you know entity framework is an ORM tool that tries to model the database to an object oriented access model. All the samples I've seen are quering directly to the database tables. So, which is the role of the views in the database now?. The views were used to model the database in a more friendly way, that is, several physical tables, one logic table. This was great for example in hidding the complex relational model on stored procedures as queryng the views inside them was much easier than reproducing the query joins over and over on each stored procedure. So the question is, why is entity framework so good if stored procedures can not take benefit of it?

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  • What mail storage should I choose for our web application; IMAP, key-valud store, rdbms, ...

    - by tvrtko
    I have to store e-mail messages for use with our application. I have "metadata" for all messages inside a relational database, but I don't feel comfortable keeping message content (gigabytes and terabytes of email data) inside a database. I'm currently using IMAP as a storage, but I have my doubts if I choose correctly. First of all there is a problem of uidvalidity and how to keep a permanent reference to message inside IMAP. Second, I'm not sure if this is the most robust solution in terms of backup/restore strategies, corruption of store, replication ... Positive side is that I can query IMAP using the headers because the data is mostly indexed. I don't know if key-value stores are a better approach (Casandra, Tokyo cabinet, redis). How they handle storing 1KB and 50MB of data. How they prevent corruption and when corruption or device failure happens how can I repair the store.

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  • Pros and cons of sorting data in DB?

    - by Roman
    Let's assume I have a table with field of type VARCHAR. And I need to get data from that table sorted alphabetically by that field. What is the best way (for performance): add sort by field to the SQL-query or sort the data when it's already fetched? I'm using Java (with Hibernate), but I can't tell anything about DB engine. It could be any popular relational database (like MySQL or MS Sql Server or Oracle or HSQL DB or any other). The amount of records in table can vary greatly but let's assume there are 5k records.

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  • SaaS Multi-tenancy Applications: How is data import/export/backup being implemented?

    - by Mark Redman
    How are applications providing import / export (or backups) of data in SaaS based multi-tenancy applications, particularly single database designs? Imports: Keeping things simple I think basic imports are useful, ie CSV to a spec (or a way of providing a mapping between CSV columns and fields in the database. Exports: In single database designs I have seen XML exports and HTML (basic sitse generated) exports of data? I would assume that XML is a better option? How does one cater for relational data? Would you reference various things within XML and provide documentation of the relationships or let users figurethis out? Are vendors providing an export/backup that can be imported back in/restored? Your comments appreciated.

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  • Query optimization using composite indexes

    - by xmarch
    Many times, during the process of creating a new Coherence application, developers do not pay attention to the way cache queries are constructed; they only check that these queries comply with functional specs. Later, performance testing shows that these perform poorly and it is then when developers start working on improvements until the non-functional performance requirements are met. This post describes the optimization process of a real-life scenario, where using a composite attribute index has brought a radical improvement in query execution times.  The execution times went down from 4 seconds to 2 milliseconds! E-commerce solution based on Oracle ATG – Endeca In the context of a new e-commerce solution based on Oracle ATG – Endeca, Oracle Coherence has been used to calculate and store SKU prices. In this architecture, a Coherence cache stores the final SKU prices used for Endeca baseline indexing. Each SKU price is calculated from a base SKU price and a series of calculations based on information from corporate global discounts. Corporate global discounts information is stored in an auxiliary Coherence cache with over 800.000 entries. In particular, to obtain each price the process needs to execute six queries over the global discount cache. After the implementation was finished, we discovered that the most expensive steps in the price calculation discount process were the global discounts cache query. This query has 10 parameters and is executed 6 times for each SKU price calculation. The steps taken to optimise this query are described below; Starting point Initial query was: String filter = "levelId = :iLevelId AND  salesCompanyId = :iSalesCompanyId AND salesChannelId = :iSalesChannelId "+ "AND departmentId = :iDepartmentId AND familyId = :iFamilyId AND brand = :iBrand AND manufacturer = :iManufacturer "+ "AND areaId = :iAreaId AND endDate >=  :iEndDate AND startDate <= :iStartDate"; Map<String, Object> params = new HashMap<String, Object>(10); // Fill all parameters. params.put("iLevelId", xxxx); // Executing filter. Filter globalDiscountsFilter = QueryHelper.createFilter(filter, params); NamedCache globalDiscountsCache = CacheFactory.getCache(CacheConstants.GLOBAL_DISCOUNTS_CACHE_NAME); Set applicableDiscounts = globalDiscountsCache.entrySet(globalDiscountsFilter); With the small dataset used for development the cache queries performed very well. However, when carrying out performance testing with a real-world sample size of 800,000 entries, each query execution was taking more than 4 seconds. First round of optimizations The first optimisation step was the creation of separate Coherence index for each of the 10 attributes used by the filter. This avoided object deserialization while executing the query. Each index was created as follows: globalDiscountsCache.addIndex(new ReflectionExtractor("getXXX" ) , false, null); After adding these indexes the query execution time was reduced to between 450 ms and 1s. However, these execution times were still not good enough.  Second round of optimizations In this optimisation phase a Coherence query explain plan was used to identify how many entires each index reduced the results set by, along with the cost in ms of executing that part of the query. Though the explain plan showed that all the indexes for the query were being used, it also showed that the ordering of the query parameters was "sub-optimal".  Parameters associated to object attributes with high-cardinality should appear at the beginning of the filter, or more specifically, the attributes that filters out the highest of number records should be placed at the beginning. But examining corporate global discount data we realized that depending on the values of the parameters used in the query the “good” order for the attributes was different. In particular, if the attributes brand and family had specific values it was more optimal to have a different query changing the order of the attributes. Ultimately, we ended up with three different optimal variants of the query that were used in its relevant cases: String filter = "brand = :iBrand AND familyId = :iFamilyId AND departmentId = :iDepartmentId AND levelId = :iLevelId "+ "AND manufacturer = :iManufacturer AND endDate >= :iEndDate AND salesCompanyId = :iSalesCompanyId "+ "AND areaId = :iAreaId AND salesChannelId = :iSalesChannelId AND startDate <= :iStartDate"; String filter = "familyId = :iFamilyId AND departmentId = :iDepartmentId AND levelId = :iLevelId AND brand = :iBrand "+ "AND manufacturer = :iManufacturer AND endDate >=  :iEndDate AND salesCompanyId = :iSalesCompanyId "+ "AND areaId = :iAreaId  AND salesChannelId = :iSalesChannelId AND startDate <= :iStartDate"; String filter = "brand = :iBrand AND departmentId = :iDepartmentId AND familyId = :iFamilyId AND levelId = :iLevelId "+ "AND manufacturer = :iManufacturer AND endDate >= :iEndDate AND salesCompanyId = :iSalesCompanyId "+ "AND areaId = :iAreaId AND salesChannelId = :iSalesChannelId AND startDate <= :iStartDate"; Using the appropriate query depending on the value of brand and family parameters the query execution time dropped to between 100 ms and 150 ms. But these these execution times were still not good enough and the solution was cumbersome. Third and last round of optimizations The third and final optimization was to introduce a composite index. However, this did mean that it was not possible to use the Coherence Query Language (CohQL), as composite indexes are not currently supporte in CohQL. As the original query had 8 parameters using EqualsFilter, 1 using GreaterEqualsFilter and 1 using LessEqualsFilter, the composite index was built for the 8 attributes using EqualsFilter. The final query had an EqualsFilter for the multiple extractor, a GreaterEqualsFilter and a LessEqualsFilter for the 2 remaining attributes.  All individual indexes were dropped except the ones being used for LessEqualsFilter and GreaterEqualsFilter. We were now running in an scenario with an 8-attributes composite filter and 2 single attribute filters. The composite index created was as follows: ValueExtractor[] ve = { new ReflectionExtractor("getSalesChannelId" ), new ReflectionExtractor("getLevelId" ),    new ReflectionExtractor("getAreaId" ), new ReflectionExtractor("getDepartmentId" ),    new ReflectionExtractor("getFamilyId" ), new ReflectionExtractor("getManufacturer" ),    new ReflectionExtractor("getBrand" ), new ReflectionExtractor("getSalesCompanyId" )}; MultiExtractor me = new MultiExtractor(ve); NamedCache globalDiscountsCache = CacheFactory.getCache(CacheConstants.GLOBAL_DISCOUNTS_CACHE_NAME); globalDiscountsCache.addIndex(me, false, null); And the final query was: ValueExtractor[] ve = { new ReflectionExtractor("getSalesChannelId" ), new ReflectionExtractor("getLevelId" ),    new ReflectionExtractor("getAreaId" ), new ReflectionExtractor("getDepartmentId" ),    new ReflectionExtractor("getFamilyId" ), new ReflectionExtractor("getManufacturer" ),    new ReflectionExtractor("getBrand" ), new ReflectionExtractor("getSalesCompanyId" )}; MultiExtractor me = new MultiExtractor(ve); // Fill composite parameters.String SalesCompanyId = xxxx;...AndFilter composite = new AndFilter(new EqualsFilter(me,                   Arrays.asList(iSalesChannelId, iLevelId, iAreaId, iDepartmentId, iFamilyId, iManufacturer, iBrand, SalesCompanyId)),                                     new GreaterEqualsFilter(new ReflectionExtractor("getEndDate" ), iEndDate)); AndFilter finalFilter = new AndFilter(composite, new LessEqualsFilter(new ReflectionExtractor("getStartDate" ), iStartDate)); NamedCache globalDiscountsCache = CacheFactory.getCache(CacheConstants.GLOBAL_DISCOUNTS_CACHE_NAME); Set applicableDiscounts = globalDiscountsCache.entrySet(finalFilter);      Using this composite index the query improved dramatically and the execution time dropped to between 2 ms and  4 ms.  These execution times completely met the non-functional performance requirements . It should be noticed than when using the composite index the order of the attributes inside the ValueExtractor was not relevant.

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  • Windows Phone7 Development: Selecting target SDK(OS) version

    - by JibW
    I am a bit confusing in selecting the target version in Windows phone7 Application development. In my Windows phone7 app I need to use a light weight relational DB Which didn't introduce with version 7.0 but SQL CE with 7.1 version. The problem is if I select the target version as 7.1, then the devices which came up with windows phone7 OS 7.0 will not be able to install this. But I heard that all the devices that came with windows phone7 OS version 7.0 is upgradable for windows OS version 7.1 for free. If this is the case then if I select the development SDK version as 7.1, then will all the windows phone7 devices be able to install this? Like to know which will be the best Target version in this case to select, before I start developing. Any guidance/ Idea is highly appreciated. Thanks...

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  • Making OR/M loosely coupled and abstracted away from other layers.

    - by Genuine
    Hi all. In an n-tier architecture, the best place to put an object-relational mapping (OR/M) code is in the data access layer. For example, database queries and updates can be delegated to a tool like NHibernate. Yet, I'd like to keep all references to NHibernate within the data access layer and abstract dependencies away from the layers below or above it. That way, I can swap or plug in another OR/M tool (e.g. Entity Framework) or some approach (e.g. plain vanilla stored procedure calls, mock objects) without causing compile-time errors or a major overhaul of the entire application. Testability is an added bonus. Could someone please suggest a wrapper (i.e. an interface or base class) or approach that would keep OR/M loosely coupled and contained in 1 layer? Or point me to resources that would help? Thanks.

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  • What are some "mental steps" a developer must take to begin moving from SQL to NO-SQL (CouchDB, Fath

    - by Byron Sommardahl
    I have my mind firmly wrapped around relational databases and how to code efficiently against them. Most of my experience is with MySQL and SQL. I like many of the things I'm hearing about document-based databases, especially when someone in a recent podcast mentioned huge performance benefits. So, if I'm going to go down that road, what are some of the mental steps I must take to shift from SQL to NO-SQL? If it makes any difference in your answer, I'm a C# developer primarily (today, anyhow). I'm used to ORM's like EF and Linq to SQL. Before ORMs, I rolled my own objects with generics and datareaders. Maybe that matters, maybe it doesn't. Here are some more specific: How do I need to think about joins? How will I query without a SELECT statement? What happens to my existing stored objects when I add a property in my code? (feel free to add questions of your own here)

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  • Creating a new plugin for mpld3

    - by sjp14051
    Toward learning how to create a new mpld3 plugin, I took an existing example, LinkedDataPlugin (http://mpld3.github.io/examples/heart_path.html), and modified it slightly by deleting references to lines object. That is, I created the following: class DragPlugin(plugins.PluginBase): JAVASCRIPT = r""" mpld3.register_plugin("drag", DragPlugin); DragPlugin.prototype = Object.create(mpld3.Plugin.prototype); DragPlugin.prototype.constructor = DragPlugin; DragPlugin.prototype.requiredProps = ["idpts", "idpatch"]; DragPlugin.prototype.defaultProps = {} function DragPlugin(fig, props){ mpld3.Plugin.call(this, fig, props); }; DragPlugin.prototype.draw = function(){ var patchobj = mpld3.get_element(this.props.idpatch, this.fig); var ptsobj = mpld3.get_element(this.props.idpts, this.fig); var drag = d3.behavior.drag() .origin(function(d) { return {x:ptsobj.ax.x(d[0]), y:ptsobj.ax.y(d[1])}; }) .on("dragstart", dragstarted) .on("drag", dragged) .on("dragend", dragended); patchobj.path.attr("d", patchobj.datafunc(ptsobj.offsets, patchobj.pathcodes)); patchobj.data = ptsobj.offsets; ptsobj.elements() .data(ptsobj.offsets) .style("cursor", "default") .call(drag); function dragstarted(d) { d3.event.sourceEvent.stopPropagation(); d3.select(this).classed("dragging", true); } function dragged(d, i) { d[0] = ptsobj.ax.x.invert(d3.event.x); d[1] = ptsobj.ax.y.invert(d3.event.y); d3.select(this) .attr("transform", "translate(" + [d3.event.x,d3.event.y] + ")"); patchobj.path.attr("d", patchobj.datafunc(ptsobj.offsets, patchobj.pathcodes)); } function dragended(d, i) { d3.select(this).classed("dragging", false); } } mpld3.register_plugin("drag", DragPlugin); """ def __init__(self, points, patch): print "Points ID : ", utils.get_id(points) self.dict_ = {"type": "drag", "idpts": utils.get_id(points), "idpatch": utils.get_id(patch)} However, when I try to link the plugin to a figure, as in plugins.connect(fig, DragPlugin(points[0], patch)) I get an error, 'module' is not callable, pointing to this line. What does this mean and why doesn't it work? Thanks. I'm adding additional code to show that linking more than one Plugin might be problematic. But this may be entirely due to some silly mistake on my part, or there is a way around it. The following code based on LinkedViewPlugin generates three panels, in which the top and the bottom panel are supposed to be identical. Mouseover in the middle panel was expected to control the display in the top and bottom panels, but updates occur in the bottom panel only. It would be nice to be able to figure out how to reflect the changes in multiple panels. Thanks. import matplotlib import matplotlib.pyplot as plt import numpy as np import mpld3 from mpld3 import plugins, utils class LinkedView(plugins.PluginBase): """A simple plugin showing how multiple axes can be linked""" JAVASCRIPT = """ mpld3.register_plugin("linkedview", LinkedViewPlugin); LinkedViewPlugin.prototype = Object.create(mpld3.Plugin.prototype); LinkedViewPlugin.prototype.constructor = LinkedViewPlugin; LinkedViewPlugin.prototype.requiredProps = ["idpts", "idline", "data"]; LinkedViewPlugin.prototype.defaultProps = {} function LinkedViewPlugin(fig, props){ mpld3.Plugin.call(this, fig, props); }; LinkedViewPlugin.prototype.draw = function(){ var pts = mpld3.get_element(this.props.idpts); var line = mpld3.get_element(this.props.idline); var data = this.props.data; function mouseover(d, i){ line.data = data[i]; line.elements().transition() .attr("d", line.datafunc(line.data)) .style("stroke", this.style.fill); } pts.elements().on("mouseover", mouseover); }; """ def __init__(self, points, line, linedata): if isinstance(points, matplotlib.lines.Line2D): suffix = "pts" else: suffix = None self.dict_ = {"type": "linkedview", "idpts": utils.get_id(points, suffix), "idline": utils.get_id(line), "data": linedata} class LinkedView2(plugins.PluginBase): """A simple plugin showing how multiple axes can be linked""" JAVASCRIPT = """ mpld3.register_plugin("linkedview", LinkedViewPlugin2); LinkedViewPlugin2.prototype = Object.create(mpld3.Plugin.prototype); LinkedViewPlugin2.prototype.constructor = LinkedViewPlugin2; LinkedViewPlugin2.prototype.requiredProps = ["idpts", "idline", "data"]; LinkedViewPlugin2.prototype.defaultProps = {} function LinkedViewPlugin2(fig, props){ mpld3.Plugin.call(this, fig, props); }; LinkedViewPlugin2.prototype.draw = function(){ var pts = mpld3.get_element(this.props.idpts); var line = mpld3.get_element(this.props.idline); var data = this.props.data; function mouseover(d, i){ line.data = data[i]; line.elements().transition() .attr("d", line.datafunc(line.data)) .style("stroke", this.style.fill); } pts.elements().on("mouseover", mouseover); }; """ def __init__(self, points, line, linedata): if isinstance(points, matplotlib.lines.Line2D): suffix = "pts" else: suffix = None self.dict_ = {"type": "linkedview", "idpts": utils.get_id(points, suffix), "idline": utils.get_id(line), "data": linedata} fig, ax = plt.subplots(3) # scatter periods and amplitudes np.random.seed(0) P = 0.2 + np.random.random(size=20) A = np.random.random(size=20) x = np.linspace(0, 10, 100) data = np.array([[x, Ai * np.sin(x / Pi)] for (Ai, Pi) in zip(A, P)]) points = ax[1].scatter(P, A, c=P + A, s=200, alpha=0.5) ax[1].set_xlabel('Period') ax[1].set_ylabel('Amplitude') # create the line object lines = ax[0].plot(x, 0 * x, '-w', lw=3, alpha=0.5) ax[0].set_ylim(-1, 1) ax[0].set_title("Hover over points to see lines") linedata = data.transpose(0, 2, 1).tolist() plugins.connect(fig, LinkedView(points, lines[0], linedata)) # second set of lines exactly the same but in a different panel lines2 = ax[2].plot(x, 0 * x, '-w', lw=3, alpha=0.5) ax[2].set_ylim(-1, 1) ax[2].set_title("Hover over points to see lines #2") plugins.connect(fig, LinkedView2(points, lines2[0], linedata)) mpld3.show()

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  • Replacing objects, handling clones, dealing with write logs

    - by Alix
    Hi everyone, I'm dealing with a problem I can't figure out how to solve, and I'd love to hear some suggestions. [NOTE: I realise I'm asking several questions; however, answers need to take into account all of the issues, so I cannot split this into several questions] Here's the deal: I'm implementing a system that underlies user applications and that protect shared objects from concurrent accesses. The application programmer (whose application will run on top of my system) defines such shared objects like this: public class MyAtomicObject { // These are just examples of fields you may want to have in your class. public virtual int x { get; set; } public virtual List<int> list { get; set; } public virtual MyClassA objA { get; set; } public virtual MyClassB objB { get; set; } } As you can see they declare the fields of their class as auto-generated properties (auto-generated means they don't need to implement get and set). This is so that I can go in and extend their class and implement each get and set myself in order to handle possible concurrent accesses, etc. This is all well and good, but now it starts to get ugly: the application threads run transactions, like this: The thread signals it's starting a transaction. This means we now need to monitor its accesses to the fields of the atomic objects. The thread runs its code, possibly accessing fields for reading or writing. If there are accesses for writing, we'll hide them from the other transactions (other threads), and only make them visible in step 3. This is because the transaction may fail and have to roll back (undo) its updates, and in that case we don't want other threads to see its "dirty" data. The thread signals it wants to commit the transaction. If the commit is successful, the updates it made will now become visible to everyone else. Otherwise, the transaction will abort, the updates will remain invisible, and no one will ever know the transaction was there. So basically the concept of transaction is a series of accesses that appear to have happened atomically, that is, all at the same time, in the same instant, which would be the moment of successful commit. (This is as opposed to its updates becoming visible as it makes them) In order to hide the write accesses in step 2, I clone the accessed field (let's say it's the field list) and put it in the transaction's write log. After that, any time the transaction accesses list, it will actually be accessing the clone in its write log, and not the global copy everyone else sees. Like this, any changes it makes will be done to the (invisible) clone, not to the global copy. If in step 3 the commit is successful, the transaction should replace the global copy with the updated list it has in its write log, and then the changes become visible for everyone else at once. It would be something like this: myAtomicObject.list = updatedCloneOfListInTheWriteLog; Problem #1: possible references to the list. Let's say someone puts a reference to the global list in a dictionary. When I do... myAtomicObject.list = updatedCloneOfListInTheWriteLog; ...I'm just replacing the reference in the field list, but not the real object (I'm not overwriting the data), so in the dictionary we'll still have a reference to the old version of the list. A possible solution would be to overwrite the data (in the case of a list, empty the global list and add all the elements of the clone). More generically, I would need to copy the fields of one list to the other. I can do this with reflection, but that's not very pretty. Is there any other way to do it? Problem #2: even if problem #1 is solved, I still have a similar problem with the clone: the application programmer doesn't know I'm giving him a clone and not the global copy. What if he puts the clone in a dictionary? Then at commit there will be some references to the global copy and some to the clone, when in truth they should all point to the same object. I thought about providing a wrapper object that contains both the cloned list and a pointer to the global copy, but the programmer doesn't know about this wrapper, so they're not going to use the pointer at all. The wrapper would be like this: public class Wrapper<T> : T { // This would be the pointer to the global copy. The local data is contained in whatever fields the wrapper inherits from T. private T thisPtr; } I do need this wrapper for comparisons: if I have a dictionary that has an entry with the global copy as key, if I look it up with the clone, like this: dictionary[updatedCloneOfListInTheWriteLog] I need it to return the entry, that is, to think that updatedCloneOfListInTheWriteLog and the global copy are the same thing. For this, I can just override Equals, GetHashCode, operator== and operator!=, no problem. However I still don't know how to solve the case in which the programmer unknowingly inserts a reference to the clone in a dictionary. Problem #3: the wrapper must extend the class of the object it wraps (if it's wrapping MyClassA, it must extend MyClassA) so that it's accepted wherever an object of that class (MyClass) would be accepted. However, that class (MyClassA) may be final. This is pretty horrible :$. Any suggestions? I don't need to use a wrapper, anything you can think of is fine. What I cannot change is the write log (I need to have a write log) and the fact that the programmer doesn't know about the clone. I hope I've made some sense. Feel free to ask for more info if something needs some clearing up. Thanks so much!

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  • Reading data from database and binding them to custom ListView

    - by N.K.
    I try to read data from a database i have made and to show some of the data in a row at a custom ListView. I can not understand what is my mistake. This is my code: public class EsodaMainActivity extends Activity { public static final String ROW_ID = "row_id"; //Intent extra key private ListView esodaListView; // the ListActivitys ListView private SimpleCursorAdapter esodaAdapter; // adapter for ListView DatabaseConnector databaseConnector = new DatabaseConnector(EsodaMainActivity.this); // called when the activity is first created @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_esoda_main); esodaListView = (ListView)findViewById(R.id.esodaList); esodaListView.setOnItemClickListener(viewEsodaListener); databaseConnector.open(); //Cursor cursor= databaseConnector.query("esoda", new String[] // {"name", "amount"}, null,null,null); Cursor cursor=databaseConnector.getAllEsoda(); startManagingCursor(cursor); // map each esoda to a TextView in the ListView layout // The desired columns to be bound String[] from = new String[] {"name","amount"}; // built an String array named "from" //The XML defined views which the data will be bound to int[] to = new int[] { R.id.esodaTextView, R.id.amountTextView}; // built an int array named "to" // EsodaMainActivity.this = The context in which the ListView is running // R.layout.esoda_list_item = Id of the layout that is used to display each item in ListView // null = // from = String array containing the column names to display // to = Int array containing the column names to display esodaAdapter = new SimpleCursorAdapter (this, R.layout.esoda_list_item, cursor, from, to); esodaListView.setAdapter(esodaAdapter); // set esodaView's adapter } // end of onCreate method @Override protected void onResume() { super.onResume(); // call super's onResume method // create new GetEsodaTask and execute it // GetEsodaTask is an AsyncTask object new GetEsodaTask().execute((Object[]) null); } // end of onResume method // onStop method is executed when the Activity is no longer visible to the user @Override protected void onStop() { Cursor cursor= esodaAdapter.getCursor(); // gets current cursor from esodaAdapter if (cursor != null) cursor.deactivate(); // deactivate cursor esodaAdapter.changeCursor(null); // adapter now has no cursor (removes the cursor from the CursorAdapter) super.onStop(); } // end of onStop method // this class performs db query outside the GUI private class GetEsodaTask extends AsyncTask<Object, Object, Cursor> { // we create a new DatabaseConnector obj // EsodaMainActivity.this = Context DatabaseConnector databaseConnector = new DatabaseConnector(EsodaMainActivity.this); // perform the db access @Override protected Cursor doInBackground(Object... params) { databaseConnector.open(); // get a cursor containing call esoda return databaseConnector.getAllEsoda(); // the cursor returned by getAllContacts() is passed to method onPostExecute() } // end of doInBackground method // here we use the cursor returned from the doInBackground() method @Override protected void onPostExecute(Cursor result) { esodaAdapter.changeCursor(result); // set the adapter's Cursor databaseConnector.close(); } // end of onPostExecute() method } // end of GetEsodaTask class // creates the Activity's menu from a menu resource XML file @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.esoda_menu, menu); // inflates(eµf?s?) esodamainactivity_menu.xml to the Options menu return true; } // end of onCreateOptionsMenu() method //handles choice from options menu - is executed when the user touches a MenuItem @Override public boolean onOptionsItemSelected(MenuItem item) { // creates a new Intent to launch the AddEditEsoda Activity // EsodaMainActivity.this = Context from which the Activity will be launched // AddEditEsoda.class = target Activity Intent addNewEsoda = new Intent(EsodaMainActivity.this, AddEditEsoda.class); startActivity(addNewEsoda); return super.onOptionsItemSelected(item); } // end of method onPtionsItemSelected() // event listener that responds to the user touching a esoda's name in the ListView OnItemClickListener viewEsodaListener = new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) { // create an intent to launch the ViewEsoda Activity Intent viewEsoda = new Intent(EsodaMainActivity.this, ViewEsoda.class); // pass the selected esoda's row ID as an extra with the Intent viewEsoda.putExtra(ROW_ID, arg3); startActivity(viewEsoda); // start viewEsoda.class Activity } // end of onItemClick() method }; // end of viewEsodaListener } // end of EsodaMainActivity class The statement: Cursor cursor=databaseConnector.getAllEsoda(); queries all data (columns) From the data I want to show at my custom ListView 2 of them: "name" and "amount". But I still get a debugger error. Please help.

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  • Can I expose MySQL data using PHP and OData?

    - by user359796
    As I understand it, OData is just a standardized way to expose relational data RESTfully. If I've got a PHP application, it should be able to process those RESTful requests and manipulate a MySQL database based on the request data and then return an ATOM feed. First, are the preceeding statements correct? Second, does a PHP library to do this already exist or would I have to create my own? If I have completely misunderstood these technologies and my question doesn't make sense, please feel free to let me know.

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  • Zip Code to City/State and vice-versa in a database?

    - by Simucal
    I'm new to SQL and relational databases and I have what I would imagine is a common problem. I'm making a website and when each user submits a post they have to provide a location in either a zip code or a City/State. What is the best practice for handling this? Do I simply create a Zip Code and City and State table and query against them or are there ready made solutions for handling this? I'm using SQL Server 2005 if it makes a difference. I need to be able to retrieve a zip code given a city/state or I need to be able to spit out the city state given a zip code.

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  • Usual hibernate performance pitfall

    - by Antoine Claval
    Hi, We have just finish to profile our application. ( she's begin to be slow ). the problem seems to be "in hibernate". It's a legacy mapping. Who work's, and do it's job. The relational shema behind is ok too. But some request are slow as hell. So, we would appreciate any input on common and usual mistake made with hibernate who end up with slow response. Exemple : Eager in place of Lazy can change dramaticly the response time....

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  • Retrieving data from database. Retrieve only when needed or get everything?

    - by RHaguiuda
    I have a simple application to store Contacts. This application uses a simple relational database to store Contact information, like Name, Address and other data fields. While designing it, I question came to my mind: When designing programs that uses databases, should I retrieve all database records and store them in objects in my program, so I have a very fast performance or I should always gather data only when required? Of course, retrieving all data can only be done if it`s not too many, but do you use this approach when you make sure that the database will be small (< 300 records for example)? I have designed once a similar application that fetches data only when needed, but that was slow (using a Access database). Thanks for all help.

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  • What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

    - by Seun Osewa
    I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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  • I know the big picture but can't put it in place

    - by Simbilim
    Hi, I'm interested in web development and by that I mean the bigger projects like facebook or twitter. I know the basics of java, css, php and mysql. I know there is a lot more out there. I read about it. But I don't know what the purpose is and how to put in place. Things like: Scribe, thrift, casandra, Unix/Linux, shell/perl/python scripting, PostgreSQL, MongoDB, non-relational NoSQL datastores, JVM, nginx I want to know why they need it, how they use it and what te purpose is. What I need is a book like technical background of facebook for dummies or so. Are there any books or websites that explain this from scratch? Thank you!

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  • What open source document-oriented database system is most mature for Windows usage?

    - by jdk
    After using relational databases as back-end storage all my Windows programming life (currently .NET), I want to experiment with a document-oriented database by this Wikipedia definition; it can be standalone or layered over an existing non-commercial database system. What open source document-oriented database solution would you recommend from your own experience and why? A nice to have would be a .NET provider. Admittedly this is somewhat subjective and potentially argumentative so keep it real folks and I'll do the same - also your answers will be invaluable to others looking into document-oriented databases for the first time on Windows. I'm sure the overall value of your answers will outweigh any biases. Thanks.

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  • Unique constraint on more than 10 columns

    - by tk
    I have a time-series simulation model which has more than 10 input variables. The number of distinct simulation instances would be more than 1 million, and each simulation instance generates a few output rows every day. To save the simulation result in a relational database, i designed tables like this. Table SimulationModel { simul_id : integer (primary key), input0 : string or numeric, input1 : string or numeric, ...} Table SimulationOutput { dt : DateTime (primary key), simul_id : integer (primary key), output0 : numeric, ...} My question is, is it fine to put an unique constraint on all of the input columns of SimulationModel table? If it is not a good idea, then what kind of other options do i have to make sure each model is unique?

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  • Solution for distributing MANY simple network tasks?

    - by EmpireJones
    I would like to create some sort of a distributed setup for running a ton of small/simple REST web queries in a production environment. For each 5-10 related queries which are executed from a node, I will generate a very small amount of derived data, which will need to be stored in a standard relational database (such as PostgreSQL). What platforms are built for this type of problem set? The nature, data sizes, and quantities seem to contradict the mindset of Hadoop. There are also more grid based architectures such as Condor and Sun Grid Engine, which I have seen mentioned. I'm not sure if these platforms have any recovery from errors though (checking if a job succeeds). What I would really like is a FIFO type queue that I could add jobs to, with the end result of my database getting updated. Any suggestions on the best tool for the job?

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  • How to structure opening hours of a place? May-be there's even an ontology for it?

    - by Ago
    Does anyone know any ontology which specifies opening hours of places? For example, I have a museum, which has 2 seasons. For low season (season start and end is specified), it is opened 10.00 - 18.00 on weekdays and 10-16 on saturday (on sunday it's closed), for high season it's opened 10-20 on weekdays and 10-18 on weekend. If there is no ontology, may-be people have experience, how best to structure information like that? I'm describing information in RDF. But whatever comments are welcome (even if you have relational database which holds given data). Thanks

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  • Using methods on 2 input files - 2nd is printing multiple times - Java

    - by Aaa
    I have the following code to read in text, store in a hashmap as bigrams (with other methods to sort them by frequency and do v. v. basic additive smoothing. I had it working great for one language input file (english) and then I want to expand it for the second language input file (japanese - doens;t matter what it is I suppose) using the same methods but the Japanese bigram hashmap is printing out 3 times in a row with diff. values. I've tried using diff text in the input file, making sure there are no gaps in text etc. I've also put print statements at certain places in the Japanese part of the code to see if I can get any clues but all the print statements are printing each time so I can't work out if it is looping at a certain place. I have gone through it with a fine toothcomb but am obviously missing something and slowly going crazy here - any help would be appreciated. thanks in advance... package languagerecognition2; import java.lang.String; import java.io.InputStreamReader; import java.util.*; import java.util.Iterator; import java.util.List.*; import java.util.ArrayList; import java.util.AbstractMap.*; import java.lang.Object; import java.io.*; import java.util.Enumeration; import java.util.Arrays; import java.lang.Math; public class Main { /** public static void main(String[] args) { //training English ----------------------------------------------------------------- File file = new File("english1.txt"); StringBuffer contents = new StringBuffer(); BufferedReader reader = null; try { reader = new BufferedReader(new FileReader(file)); String test = null; //test = reader.readLine(); // repeat until all lines are read while ((test = reader.readLine()) != null) { test = test.toLowerCase(); char[] charArrayEng = test.toCharArray(); HashMap<String, Integer> hashMapEng = new HashMap<String, Integer>(bigrams(charArrayEng)); LinkedHashMap<String, Integer> sortedListEng = new LinkedHashMap<String, Integer>(sort(hashMapEng)); int sizeEng=sortedListEng.size(); System.out.println("Total count of English bigrams is " + sizeEng); LinkedHashMap<String, Integer> smoothedListEng = new LinkedHashMap<String, Integer>(smooth(sortedListEng, sizeEng)); //print linkedHashMap to check values Set set= smoothedListEng.entrySet(); Iterator iter = set.iterator ( ) ; System.out.println("Beginning English"); while ( iter.hasNext()) { Map.Entry entry = ( Map.Entry ) iter.next ( ) ; Object key = entry.getKey ( ) ; Object value = entry.getValue ( ) ; System.out.println( key+" : " + value); } System.out.println("End English"); }//end while }//end try catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (reader != null) { reader.close(); } } catch (IOException e) { e.printStackTrace(); } } //End training English----------------------------------------------------------- //Training japanese-------------------------------------------------------------- File file2 = new File("japanese1.txt"); StringBuffer contents2 = new StringBuffer(); BufferedReader reader2 = null; try { reader2 = new BufferedReader(new FileReader(file2)); String test2 = null; //repeat until all lines are read while ((test2 = reader2.readLine()) != null) { test2 = test2.toLowerCase(); char[] charArrayJap = test2.toCharArray(); HashMap<String, Integer> hashMapJap = new HashMap<String, Integer>(bigrams(charArrayJap)); //System.out.println( "bigrams stage"); LinkedHashMap<String, Integer> sortedListJap = new LinkedHashMap<String, Integer>(sort(hashMapJap)); //System.out.println( "sort stage"); int sizeJap=sortedListJap.size(); //System.out.println("Total count of Japanese bigrams is " + sizeJap); LinkedHashMap<String, Integer> smoothedListJap = new LinkedHashMap<String, Integer>(smooth(sortedListJap, sizeJap)); System.out.println( "smooth stage"); //print linkedHashMap to check values Set set2= smoothedListJap.entrySet(); Iterator iter2 = set2.iterator(); System.out.println("Beginning Japanese"); while ( iter2.hasNext()) { Map.Entry entry2 = ( Map.Entry ) iter2.next ( ) ; Object key = entry2.getKey ( ) ; Object value = entry2.getValue ( ) ; System.out.println( key+" : " + value); }//end while System.out.println("End Japanese"); }//end while }//end try catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (reader2 != null) { reader2.close(); } } catch (IOException e) { e.printStackTrace(); } } //end training Japanese--------------------------------------------------------- } //end main (inner)

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  • Storing Data as XML BLOB

    - by NBrowne
    Hi, At the moment the team i am working with is looking into the possibility of storing data which is entered by users from a series of input wizard screens as an XML blob in the database. the main reason for this being that i would like to write the input wizard as a component which can be brought into a number of systems without having to bring with it a large table structure. To try to clarify if the wizard has 100 input fields (for example) then if i go with the normal relational db structure then their will be a 1 to 1 relationship so will have 100 columns in database. So to get this working in another system will have to bring the tables,strore procedures etc into the new system. I have a number of reservations about this but i would like peoples opinions?? thanks

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  • ADO.NET DataService Exception

    - by Ravi
    Hi, I am working on C#.Net with ADO.NET Dataservice. I try to update one record to relational tabel, when I reach context.SetLink() I am getting exception("The context is not currently tracking the entity"). I don't know how to solve this problem. My code is specified below. LogNote dbLogNote =logNote; LogSubSession dbLogSubSession = (from p in context.LogSubSession where p.UID == logNote.SubSessionId select p).First<LogSubSession>() as LogSubSession; context.AddToLogNote(dbLogNote); dbLogNote.LogSubSession = dbLogSubSession; context.SetLink(dbLogNote, "LogSubSession", dbLogSubSession); context.SaveChanges(); Here LogSubSession is a primary table and LogNote is a foreign table. I am updating data into foreign table based on primary key table. Thanks

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  • How do I take the advantage of the variable column key/value structure of Cassandra

    - by icejade
    If I have to predefine all the columns, how do I take the advantage of the variable column key/value structure of cassandra? If I use update table command, it will insert null for all the rows which don't have that column. This is same as relational DB. For example, for contact column family, I have name, phone, email. I have 100 contacts have all 3 field. Then number 101 contact has skype id which I want to add. If I use insert statement, it won't let me add skypeid since it's not defined in the CF. So I have to run alter statement to change the CF, then all the first 100 contacts will have a null field for each of them.

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