Influx 2.0 queries with Grafana

Influx 2.0 (flux) queries in grafana are a little on the messy side.  Here are a comple of examples that might be useful.


Here is an example of summing up a number of fields for display on a "single stat" panel widget

from(bucket: "powermon")

|> range(start: -1h)

|> filter(fn: (r) => r._measurement == "modbus")

|> filter(fn: (r) => r._field == "pv1" or r._field == "pv2" or r._field == "pv3" or r._field == "pv4" or r._field == "pv5" or r._field == "pv6" or r._field == "pv7")

|> last()

|>keep(columns:["_value"])

|> sum()

When playing with graphs, things are more or less as you'd expect:

from(bucket: "powermon")

|> range(${range})

|> filter(fn: (r) => r._measurement == "modbus")

|> filter(fn: (r) => r._field == "pv1" or r._field == "pv2" or r._field == "pv3" or r._field == "pv4" or r._field == "pv5" or r._field == "pv6" or r._field == "pv7")

|> aggregateWindow(every: 1m, fn: (tables=<-, column) => {

return tables |> mean(column: column) |> map(fn: (r) => ({r with _value: r._value*1000.0}))

})

|> yield(name: "mean")

 

 

Table-driven holes in Solidworks

I recently had occasion to want to create a series of holes in Solidworks.  The hole definition isn't complicated but it has a few parts to it - the specific shape I am going for cups an LED and couples it to an acrylic light pipe.  This is embedded into a large plastic plate, which could be a base plate or perhaps a cover.  The hole shape, in section view, looks like this:

The hole shape is made by drawing a 2D profile them revolving it around the centerline, which in the view below is the on the left side.  The 2D shape, in profile, makes up one half of the hole.

I needed nine such holes but not on a regular pattern.  It turns out there is a way to duplicate features in SolidWorks but using it is a little confusing - the manual page and tutorial are pretty short.  I'm documenting the process here so I can give some tips (and remind myself how to do this a year from now when I probably will have forgotten the whole thing).

The first thing you need to do is to create a coordinate system.  This was for me one of the confusing parts.  The coordinate system defines an orientation (which direction is X, Y, and Z, including which way is positive and negative) and an origin (what point corresponds to coordinates 0,0,0).  There are a few ways to define a coordinate system.  For this, I'm setting an origin, Y, and Z.  From those the software figures our which way is X.

To begin, I've drawn the 'base' into which all these holes will be extruded:

I started the hole by using the hole wizard, but hole wizard isn't magical.  All it does is creates two 2D sketches then revolves the second one around a centerline:

The first sketch does nothing but define the center point of the hole.  The second sketch is the 2D hole shape listed above.

Next, what I did was to create a reference point that marks the center of the hole - essentially what this does is to bring the centerpoint of the hole out of the sketch and up to the 3D drawing.

Now I have my base with one hole in it:

The next step is to define a coordinate system.  In my case, the origin is the center of the hole.  This mean that in my table, the first hole will be at location 0,0 and all the "copies" will be relative to that:

Next I create the table.  I did this in excel.  By default the units will be in the same units as your document, but you can specify 'in' or 'mm' (or any other SolidWorks unit) if you like:

Finally, create the pattern:

A couple of things to note:

• The coordinate system is placed at the point we created, so that's 0,0 - all the coordinates in the table will be relative to that
• The "Feature" is the hole, created by the hole wizard (then its shape modified by me)

The result is my baseplate with all of the holes replicated at my X,Y locations:

Now don't ask me what it is (it's a secret) - I'll tell you next month!

Which is better?

I am making a Spring Boot app using Spring Data that has, as part of its function, an embedded wiki. Individual wiki pages have workflows associated with them. Rather than maintain a list of parent/child relationships for pages I'm using an implied hierarchical structure based on the 'path' columns that serve as the coordinates for each page. The hard part is finding only the direct descendants of each page. To do this, I look for paths that include the 'parent' but have no other path separators. In other words, descendants of labs would include /labs/electronics and /labs/bio but would not include /labs/electronics/equipment because, while equipment is a descendant of /labs it is not a direct descendant.

To accomplish this, I do two things:

• Find the paths that begin with the parent's path, including trailing slash, for example /labs/. This selects all descendants of the parent.
• Of those, find the ones who have NO OTHER SLASHES beyond the parent. This selects only the direct descendants.

Here are two ways to do it, both produce identical results:

Using JPQL

@Query("select w from WikiPage w " +
    " where w.path like concat(:path, '/', '%') " +
    " AND LOCATE('/', w.path, length(:path)+2) = 0")
public List<WikiPage>
    findDirectChildrenOfUsingAnnotationQuery(@Param("path") String path);

Using the Java-based Query DSL

@Override
public List<WikiPage> findDirectChildrenOfUsingQueryDSL(String searchPath) {
    CriteriaBuilder builder = em.getCriteriaBuilder();
    CriteriaQuer<WikiPage> query = builder.createQuery(WikiPage.class);
    Root<WikiPage> wikiPage_root = query.from(WikiPage.class);

    Expression<String> wikiPage_path = wikiPage_root.get("path");
    Predicate startsWithPath = builder.like(wikiPage_path,  searchPath + "/%");

    Expression<Integer> slashLocation = builder.locate(wikiPage_path, "/",
        searchPath.length()+2);
    Predicate noMoreDescendants = builder.equal(slashLocation, 0);

    query = query.where(builder.and(startsWithPath, noMoreDescendants));
    return em.createQuery(query.select(wikiPage_root)).getResultList();
}

Reasons to use the Java DSL

• It is more refactorable ... but, a good IDE like IntelliJ can refactor JPQL just fine
• It's more typesafe ... but not completely so, and again, IntelliJ does a pretty good job. You could even argue that it does better, because the Java DSL can't tell that "path" is a valid attribute of WikiPage, but in JPQL it could
• Compiler-time errors if you screw up ... but again, IntelliJ already tells me if my JPQL is invalid
• Certain operations - like the concat and strlen - are arguably better handled in java than by the db engine

The Java DSL is definitely harder to read. But I have a distaste for 'magical strings' which includes JPQL in a @Query annotation.

Thoughts?

Dynamic baseref with angular 2

Angular 2 determines how to load 'relative' links using this tag in the main index:

<base href="/">&lt

This isn't a great thing if you want to deploy to other than the root directory of a server. You can find many examples of this causing grief for developers.

Short of manually changing base href before you deploy, the most common solution seems to be to have a little bit of javascript emit the base href into the document before angular loads. Yuck. I managed to work up a more D.I. way to do this that I'll share. No guarantees that this is going to keep working in subsequent RCs (I'm still on 2.0.0-rc.5):

import {RouterModule} from '@angular/router';
import {APP_BASE_HREF} from '@angular/common';
import {ModuleWithProviders} from '@angular/core';
/* all your other imports */


const appRoutingProviders: any[] = [
  {
    provide: APP_BASE_HREF,
    useFactory: () => {
      return window.location.pathname;
    }, deps: [  ]
  }
];
const routingModule: ModuleWithProviders = RouterModule.forRoot(routingTable, {enableTracing: false, useHash: true});

@NgModule({
  declarations: [
    AppComponent, /* list all your other components here */
  ],
  imports: [
    BrowserModule,
    CommonModule,
    FormsModule,
    HttpModule,
    routingModule
  ],
  providers: [appRoutingProviders],
  bootstrap: [AppComponent],
  entryComponents: [AppComponent]
})
export class AppModule {
}

The basic idea is to build a bridge into the initial path then use that as the base. I've been looking for a less error-prone mechanism and haven't found it yet - certainly this could be a little more robust in the form of error checking. If you're like me and want to deploy by scp then it's better than the alternative, having to edit index.html based on where you deploy.

Changing the catalog on a JdbcTemplate (with Spring)

I had a requirement to change the catalog (i.e. database) with JdbcTemplate. I searched around for a while for an answer and, as is often the case, found a solution scattered across several Stack Overflow and other posts. My configuration is:

• Spring Framework 4.2.5.RELEASE
• spring-jdbc (for JdbcTemplate)
• tomcat-jdbc 8.0.18 (for org.apache.tomcat.jdbc.pool.DataSource)

The key to making this all work is to to extend Spring's DelegatingDataSource and override getConnection() to set the catalog you want:

public class CatalogSpecificDataSource extends DelegatingDataSource {

    private final String catalog;

    public CatalogSpecificDataSource(DataSource orig, String catalog) {
        super(orig);
        this.catalog = catalog;
    }

    @Override
    public Connection getConnection() throws SQLException {
        Connection conn = super.getConnection();
        conn.setCatalog(catalog);
        return conn;
    }
}

The next problem is cleanup: how do you ensure that the connection is reset to the default catalog once it's placed into the pool? The answer is in the tomcat connection pool configuration:

    PoolProperties p = new PoolProperties();
    p.setDefaultCatalog("customers");
    /*
     * set your connection properties here - driver, connection string, etc.
     * then, when you're done with that, add the interceptors
     */
    p.setJdbcInterceptors(
        org.apache.tomcat.jdbc.pool.interceptor.ConnectionState.class.getName() + ";" +
        org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer.class.getName());
    DataSource datasource = new DataSource();
    datasource.setPoolProperties(p);

The ConnectionState interceptor remembers if you changed the catalog and will set it back. When you create your JdbcTemplate you can now:

    JdbcTemplate t = new CatalogDataSource(realDataSource, "someOtherCatalog");

or use Spring's idea of assisted injection. To do that:

Step 1. Create a factory interface

public interface CatalogSpecificDataSourceFactory {
    javax.sql.DataSource getDatasource(String catalog);
}

Step 2. Create a spring bean configuration:

    @Bean
    @Scope(BeanDefinition.SCOPE_PROTOTYPE)
    public CatalogSpecificDataSourceFactory getCatalogSpecificDatasourceFactory() {
        return catalog -> new CatalogSpecificDataSource(getCatalogSpecificDatasource(), catalog);
    }

Step 3. When you want to use it, inject a CatalogSpecificDataSourceFactory then use it to create your Datasource:

    DataSource ds = catalogSpecificDataSoruceFactory.getCatalogSpecificDatasource("booger");
    JdbcTemplate t = new JdbcTemplate(ds);

Or, if you want to get even fancier, set up another assisted factory. In my case, following the assisted injection pattern once again:

    public interface BatchMissionWriterFactory {
        BatchMissionWriter create(String databaseName);
    }

    /* then, in the config: */
    @Bean
    @Scope(BeanDefinition.SCOPE_PROTOTYPE)
    public BatchWidgetWriterFactory getBatchMissionWriterFactory()
    {
        return catalog -> new BatchWidgetWriterFactory (getCatalogDataSourceFactory().getCatalogSpecificDatasource(catalog));
    }

As usual, hope this is helpful to someone - feedback welcome.

Reverse engineering a hot tub

I changed the water in my hot tub today and so I had a lot of time on my hands, so I took the controller cover off and tried to figure out how it works. My main purpose was to try to figure out how the control panel interfaces, mainly so that I can contemplate some kind of remote monitoring interface. I know that some models of Balboa controllers have WiFi options, so I figured there must be a communications interface somewhere. There definitely is. The existing (very simple) control panel is connected via an 8-pin RJ-45, and there's a spare one right next to it. There is one removable chip on the board labeled with something looking like a version number. I peeled the sticker off and, surprise it's a PIC18F2420 microcontroller. That's great - I already have programming tools and a C compiler for that. My next step is to try to find a schematic for this board. If I can do that then the feasibility of entirely replacing the control software is high. The hardest part probably would be figuring out how to talk to their existing control panel.

Angular Directives as ES6 Classes part 2 - Scopes

Expanding on my previous post about writing directives as ES6 classes, I had a reason today to figure out scope-to-object binding. The situation is as follows. I have an ng-view with a template that includes nvd3:

    <graph tag='tag_identifier'>
        <nvd3 options='hist.options' data='hist.data' api='hist.api' ...>
    </graph>

The 'tag' attribute is an identifier for the thing being graphed (it will be fetched using ngResource) and 'api' is a reference to the nvd3 api. I will need this to call methods, such as refresh(), inside the nvd3 directive, so I have to pass these through. Inside nvd3, the scope is declared like this:

    scope: {
        data: '=',
        options: '=',
        api: '=?',
        events: '=?',
        config: '=?'
    }

but I don't want data, options, and api bound to my scope, I want them bound to my controller. The answer is described pretty well by Pascal Precht in his post Exploring Angular 1.3: Binding to Directive Controllers. This works equally well in Angular 1.4.7. I modified my registration function as follows:

    static register(module) {
        module.directive('graph', [ ()=> {
            return {
                restrict: 'AE',
                transclude: false,
                replace: true,
                controller: GraphDirectiveController,
                controllerAs: 'hist',
                scope: {}, /* true, false, or isolate */
                bindToController: {
                    'tag': '@tag',
                    'api': '=api'
                },
                templateUrl: "views/graph_widget.html",
                link: function (scope, elem, attrs, ctrl) {
                    /* set 'options' and 'data': */
                    ctrl.initGraphOptions();
                }
            };
        }]);
    }

When it comes to the lifecycle, three things are going to happen:

• Instantiation - first, angular will create an instance of your controller
• Setters - next, it will bind what used to be a scope to your controller instance
• link() - this is your chance to do any post-initialization after bindings are set up

Whatever you do, you should definitely not depend on your setters getting called in any particular order. As a directive author, it would not be very nice of you to ask your users to only write attributes in a certain order. That's the main reason to use the link function just to trigger your controller to do any post-binding setup it needs to do. In my case, this means making sure that the api has been initialied before calling initGraphOptions(), which sets this.data and this.options. (Since we're now binding the scope to the controller, that's it!) Just pay attention to the lifecycle and if things get confusing, remember this is ES6 so you can always add explicit setters to your controller and log what's happening:

    set api(_api) {
        console.log("Setting nvd3 API");
        this._api = _api;
    }