1 00:00:01,170 --> 00:00:07,680 So we're finally at the point where we can send some data from our handlers to go line templates, and 2 00:00:07,680 --> 00:00:09,330 that's not a very difficult thing to do. 3 00:00:09,360 --> 00:00:11,840 It took us a while to get here, but we're finally going to do it. 4 00:00:12,090 --> 00:00:13,860 So let's think about how that happens. 5 00:00:14,630 --> 00:00:15,720 I have these handlers. 6 00:00:15,720 --> 00:00:18,810 I mean, handlers, Dutko, I have I have two handlers right now. 7 00:00:18,810 --> 00:00:24,330 One called home and one called about and inside those handlers right now, all I'm doing is rendering 8 00:00:24,330 --> 00:00:24,870 a template. 9 00:00:24,870 --> 00:00:26,220 I'm not doing anything with them. 10 00:00:26,340 --> 00:00:29,250 I'm just reading a template from disk storing in the template cache. 11 00:00:29,700 --> 00:00:33,930 And every time the appropriate handler is called, I serve the appropriate template. 12 00:00:34,470 --> 00:00:35,330 And that's pretty good. 13 00:00:35,610 --> 00:00:37,680 But there are a lot of situations. 14 00:00:37,680 --> 00:00:39,660 For example, let's have a look at the about page. 15 00:00:40,200 --> 00:00:50,370 I might perform some business logic here, which gives me some data and then I need to send the data 16 00:00:50,370 --> 00:00:51,300 to the template. 17 00:00:51,870 --> 00:00:53,420 I don't have anywhere to do that right now. 18 00:00:53,460 --> 00:00:57,280 I have this function render template and I want to send it some data. 19 00:00:57,810 --> 00:01:03,120 So if you actually look at the render template function, it only has two arguments the response rate, 20 00:01:03,220 --> 00:01:08,190 which it has to have so it can actually have the somewhere to send the the finished webpage, the name 21 00:01:08,190 --> 00:01:11,580 of the template, but there's nowhere to actually pass data to it. 22 00:01:11,760 --> 00:01:17,880 If I had some data here, if I had a third parameter, I would actually be passing it right here on 23 00:01:17,880 --> 00:01:21,300 the part where I execute those bytes stored in a bytes buffer. 24 00:01:22,080 --> 00:01:27,870 I would pass the data in there and the execute function would take that data and put it in the correct 25 00:01:27,870 --> 00:01:29,510 place in the actual template. 26 00:01:29,910 --> 00:01:34,800 So clearly I need something to put here, but what kind of data am I going to be sending? 27 00:01:34,800 --> 00:01:35,850 It might be a date. 28 00:01:35,850 --> 00:01:37,140 It might be a string. 29 00:01:37,290 --> 00:01:40,560 It could be a full object representing a user. 30 00:01:40,680 --> 00:01:41,610 It could be anything. 31 00:01:41,610 --> 00:01:43,070 I have no idea what it's going to be. 32 00:01:43,620 --> 00:01:45,270 So what am I going to put here? 33 00:01:45,270 --> 00:01:51,150 I can't just say, well, I might have seventy five different kinds of data, therefore I'll have seventy 34 00:01:51,150 --> 00:01:58,580 five parameters to passing this in as parameters to this render template function that's really inefficient. 35 00:01:58,800 --> 00:02:03,710 Instead, let's create a new type, a new type that's going to hold template data. 36 00:02:04,320 --> 00:02:12,630 So right here back at handlers, I'm going to create at the top a new type and I shall call that type 37 00:02:13,230 --> 00:02:14,460 template data. 38 00:02:17,370 --> 00:02:22,320 And it's going to be a struct and it's going to hold whatever kinds of data I think I might need to 39 00:02:22,320 --> 00:02:22,800 put in there. 40 00:02:23,340 --> 00:02:25,950 So what kinds of things am I going to be sending? 41 00:02:26,220 --> 00:02:31,470 I'm definitely going to be sending string information because I'm going to probably send names and email 42 00:02:31,470 --> 00:02:33,570 addresses and all sorts of things that are strings. 43 00:02:33,870 --> 00:02:35,250 But how many might I send? 44 00:02:35,430 --> 00:02:37,290 I might send one for one template. 45 00:02:37,290 --> 00:02:39,290 I might send 20 for another template. 46 00:02:39,600 --> 00:02:45,690 So instead of just putting in a string type, let's put in a string that I'm going to define a type 47 00:02:45,690 --> 00:02:50,070 called string map, and it's going to be nothing more than a map of string string. 48 00:02:50,730 --> 00:02:53,280 So that's one thing I might be selling to templates. 49 00:02:53,730 --> 00:02:56,700 Another thing is I might be sending numbers into integers. 50 00:02:56,700 --> 00:03:00,870 So let's put an intermap in Intermap Map String. 51 00:03:04,360 --> 00:03:10,480 And then I might be sending floats, so let's put in a float bap float map, which will be a map of 52 00:03:10,480 --> 00:03:13,980 string to look things up and of type float. 53 00:03:13,990 --> 00:03:15,190 I'll just use float thirty two. 54 00:03:15,340 --> 00:03:18,130 There are 232 floats, float 32 and float sixty four. 55 00:03:18,130 --> 00:03:21,380 But we're not going to be using huge numbers of float 32 will do the trick. 56 00:03:22,060 --> 00:03:23,230 What else might I send. 57 00:03:23,560 --> 00:03:27,780 Well I might send things that are not maps, not strings, not floats. 58 00:03:27,790 --> 00:03:31,840 In fact they might be structures, they might be things that hold all kinds of other data. 59 00:03:32,350 --> 00:03:36,550 So for that one, I'm going to have a special type, which I will call simply data. 60 00:03:37,180 --> 00:03:41,200 And it's again, going to be a map and it will be a map with an index of string. 61 00:03:41,590 --> 00:03:44,530 But the actual content of that map can be anything. 62 00:03:44,710 --> 00:03:50,260 And in go when you're not sure what the data type is, you call it an interface. 63 00:03:50,260 --> 00:03:53,830 And because I'm declaring it as a type here, I have to put the curly brackets after it. 64 00:03:55,450 --> 00:03:59,590 So that's definitely something I'm going to possibly have to send and then I'm going to put some other 65 00:03:59,590 --> 00:04:03,610 ones in here just for the sake of doing them right now. 66 00:04:03,610 --> 00:04:04,720 So I don't have to do it later. 67 00:04:05,020 --> 00:04:11,260 When we get to the forms part, when we learn how to construct and post forms and handle the forum post 68 00:04:11,260 --> 00:04:17,230 in the handlers, we're actually going to have a little security token called a cross site request forgery 69 00:04:17,230 --> 00:04:17,620 token. 70 00:04:17,980 --> 00:04:19,060 We're not going to use it right now. 71 00:04:19,060 --> 00:04:24,130 And it's just a string, but it's something I want available on every page because a page might have 72 00:04:24,130 --> 00:04:25,060 a form at some point. 73 00:04:25,360 --> 00:04:26,490 So I'll declare it right now. 74 00:04:26,920 --> 00:04:29,950 RF token and it's just a string. 75 00:04:30,910 --> 00:04:34,450 And I'm also going to have some messages I send to the user. 76 00:04:34,780 --> 00:04:36,850 Some will be a success message. 77 00:04:36,850 --> 00:04:37,210 Yes. 78 00:04:37,210 --> 00:04:39,430 Your your submission to the site was successful. 79 00:04:39,430 --> 00:04:40,810 Some will be an error message. 80 00:04:40,810 --> 00:04:41,170 Oh no. 81 00:04:41,170 --> 00:04:45,880 You left an important piece out of the form and have to do it over again and some might just be a warming 82 00:04:45,910 --> 00:04:46,360 warning. 83 00:04:46,720 --> 00:04:48,580 So I'll set those up now as well. 84 00:04:48,610 --> 00:04:51,820 Flash is going to be a string. 85 00:04:52,510 --> 00:04:56,920 That's a flash flash message when I'm just posting on message, a success message or whatever to the 86 00:04:56,920 --> 00:05:03,250 end user warning will be a string and form will be a anot form. 87 00:05:04,270 --> 00:05:06,340 Error will also be a string. 88 00:05:06,640 --> 00:05:07,060 All right. 89 00:05:07,540 --> 00:05:10,470 Now I have a template data and of course I have to give it a comment. 90 00:05:11,170 --> 00:05:13,810 Good practice to keep these things up to date as you're doing them. 91 00:05:14,170 --> 00:05:22,360 Template data holds data sent from handlers to templates. 92 00:05:22,660 --> 00:05:23,030 All right. 93 00:05:23,050 --> 00:05:25,030 So I've declared this data type. 94 00:05:25,570 --> 00:05:29,980 So let's go back to our our render package. 95 00:05:30,340 --> 00:05:37,900 And now let's import or add that as a third parameter, which I will just call data or TD for template 96 00:05:37,900 --> 00:05:38,230 data. 97 00:05:38,440 --> 00:05:40,660 And it's going to be of type handlers. 98 00:05:42,750 --> 00:05:44,210 Dort templated. 99 00:05:45,360 --> 00:05:51,740 All right, I'm not using it yet, but down here where I have nil, I probably want to use it. 100 00:05:52,110 --> 00:05:59,700 So in order to do that, I have to make sure, first of all, that there is some kind of data in there, 101 00:05:59,940 --> 00:06:01,020 whatever it may be. 102 00:06:01,170 --> 00:06:02,520 Otherwise, I'm passing nil. 103 00:06:04,530 --> 00:06:08,240 So if you think about it, when I go back to my handlers right away, I have an error. 104 00:06:08,250 --> 00:06:13,620 I have an error because I'm not passing any template data and I can't pass nil because, well, I actually 105 00:06:13,620 --> 00:06:18,660 need template data so I can do that simply by passing an empty template data. 106 00:06:18,930 --> 00:06:28,650 And I can do that with a really simple bit of code and present template data and nothing inside of it. 107 00:06:31,350 --> 00:06:32,260 And I have an error. 108 00:06:32,280 --> 00:06:33,340 Let's go back over here. 109 00:06:33,570 --> 00:06:36,540 Can I use that type template as type hander's template data? 110 00:06:36,550 --> 00:06:39,530 Of course, I don't actually want to pass template data. 111 00:06:39,540 --> 00:06:42,100 I want to pass a pointer to template data. 112 00:06:42,720 --> 00:06:43,340 That's better. 113 00:06:43,620 --> 00:06:47,160 Now, when I go back here, that error should go away and I can do the same thing here. 114 00:06:47,700 --> 00:06:51,570 Ampersand template data with nothing. 115 00:06:52,320 --> 00:06:52,650 All right. 116 00:06:52,650 --> 00:06:53,820 So that should actually work. 117 00:06:54,270 --> 00:06:56,250 But we actually haven't done anything with the data yet. 118 00:06:56,260 --> 00:06:59,040 So let's try putting some logic in here. 119 00:06:59,040 --> 00:07:02,100 Let's just put on our about page. 120 00:07:02,100 --> 00:07:07,620 Let's put a string so I can say, first of all, I can't pass strings. 121 00:07:07,620 --> 00:07:12,690 Remember, template data at the top here says I can pass a string map, so let's create a map. 122 00:07:13,660 --> 00:07:21,570 I'll call it string map is a new make map, string string. 123 00:07:22,230 --> 00:07:26,190 OK, and then we'll say string map test. 124 00:07:26,250 --> 00:07:32,190 That's how I'll look it up in the template is assign the value of hello again. 125 00:07:33,240 --> 00:07:33,630 All right. 126 00:07:34,530 --> 00:07:36,300 Now I've created my string map. 127 00:07:36,310 --> 00:07:41,700 I haven't actually used it yet and I need to pass it as part of template data and template data has 128 00:07:41,700 --> 00:07:43,500 a member called String Map. 129 00:07:43,800 --> 00:07:47,880 And the value I want to assign to that is the string map I just created. 130 00:07:49,500 --> 00:07:55,500 So I've done that now in the template itself, and this is for the About Page, let's go to the about 131 00:07:55,500 --> 00:07:58,410 page and let's see if we can write that. 132 00:07:58,980 --> 00:08:06,600 Now, here's the very first time we're actually pulling any data from our handler into our template, 133 00:08:06,780 --> 00:08:08,610 and we're going to do it really straightforward. 134 00:08:12,270 --> 00:08:18,960 This came from the template and then because of the template directive, it's in those double curly 135 00:08:19,320 --> 00:08:25,530 braces, I want to look up something in the string mat and I can't just go string map and then square 136 00:08:25,530 --> 00:08:26,010 brackets. 137 00:08:26,010 --> 00:08:31,590 And the name that look we are looking for, we have to use the template syntax, which may seem a little 138 00:08:31,590 --> 00:08:33,720 awkward at first, but it works really well. 139 00:08:34,290 --> 00:08:38,070 Index from DOT string map. 140 00:08:38,910 --> 00:08:40,560 I'm looking for the value. 141 00:08:40,680 --> 00:08:42,330 What did I call it in my handler. 142 00:08:43,760 --> 00:08:52,040 Test, so back to the page test, so this says, I'm going to use the function index, I'm looking something 143 00:08:52,040 --> 00:08:54,620 up and something that has an indices or has indices. 144 00:08:55,580 --> 00:08:58,490 So index and I'm looking for string map. 145 00:08:58,490 --> 00:09:04,280 And I put that dot in front of it because the dot refers to all the data that is passed to the template. 146 00:09:04,760 --> 00:09:09,260 And I'm looking for one particular element, string map, and I'm looking for the index test. 147 00:09:10,280 --> 00:09:11,310 So let's give it a try. 148 00:09:11,840 --> 00:09:18,470 Now, the command is, of course, go run command Web Stargirl. 149 00:09:18,800 --> 00:09:22,040 And I'm going to run this and I'm going to tell you right now it's not going to work. 150 00:09:22,040 --> 00:09:29,200 And I have deliberately introduced an error into this project to show you the dreaded import cycle problem. 151 00:09:29,210 --> 00:09:30,700 Let's run it and we'll see what happens. 152 00:09:32,150 --> 00:09:37,490 Package command line arguments, imports, GitHub, Teszler, go course package handlers and render. 153 00:09:37,490 --> 00:09:40,460 And then we have import cycle not allowed. 154 00:09:40,850 --> 00:09:47,000 And this is what I was talking about earlier, what I told you, why I was putting the config into its 155 00:09:47,000 --> 00:09:47,710 own package. 156 00:09:48,500 --> 00:09:52,190 The problem here is that I have packages that are importing each other and you're not allowed to do 157 00:09:52,190 --> 00:09:52,760 that and go. 158 00:09:52,760 --> 00:09:55,100 You can do it in some languages like C++. 159 00:09:55,100 --> 00:09:58,940 You're allowed to well, you have to put some serious hacks in place to make it work. 160 00:09:58,940 --> 00:09:59,960 But you can do that. 161 00:10:00,290 --> 00:10:01,220 You can't do it. 162 00:10:01,220 --> 00:10:06,530 And go goes a little more strict and says, no, sorry, can't have packages that depend upon each other 163 00:10:06,530 --> 00:10:06,980 like that. 164 00:10:07,430 --> 00:10:08,990 And it refuses to compile. 165 00:10:08,990 --> 00:10:11,960 And the irritating thing about it is no idea. 166 00:10:11,960 --> 00:10:16,640 I have ever tried ever warned you about the import cycle while you're putting all the time into writing 167 00:10:16,640 --> 00:10:17,000 code. 168 00:10:17,150 --> 00:10:19,850 It's not until the moment you try to run it that you discover this. 169 00:10:20,030 --> 00:10:22,100 Fortunately, it's not that hard to fix. 170 00:10:22,550 --> 00:10:25,130 And the offending code here, let me hide this. 171 00:10:25,790 --> 00:10:29,330 The offending code is found in handlers and handlers. 172 00:10:29,330 --> 00:10:29,690 Yes. 173 00:10:29,690 --> 00:10:32,930 Where I have this template data, I'm going to pull that right out of there. 174 00:10:33,530 --> 00:10:34,970 We're not going to stick that in there. 175 00:10:34,970 --> 00:10:37,730 Instead, I'm going to create a new package. 176 00:10:40,320 --> 00:10:47,700 Called models, and it's where I'm going to store all the models that I'm going to use in my my application, 177 00:10:47,700 --> 00:10:51,130 and that includes database models and it includes the template data model. 178 00:10:51,660 --> 00:10:55,310 So here I'm going to create a new file and I'm not going to call it models ago. 179 00:10:55,340 --> 00:10:58,410 Let me close that and get rid of that. 180 00:10:59,290 --> 00:11:01,650 OK, I'm going to create a new model. 181 00:11:03,660 --> 00:11:04,350 And file. 182 00:11:08,780 --> 00:11:09,620 A new file. 183 00:11:10,950 --> 00:11:14,250 Called template data go. 184 00:11:15,830 --> 00:11:16,940 And I'll paste that in there. 185 00:11:17,120 --> 00:11:23,270 OK, so now I have this over where it's divorced from everything else, this will never import another 186 00:11:23,270 --> 00:11:23,710 package. 187 00:11:23,720 --> 00:11:27,940 It will only exist to be imported by packages other than itself. 188 00:11:28,550 --> 00:11:29,780 So I can handle it. 189 00:11:29,780 --> 00:11:33,830 Can't be just template data down here at line 31. 190 00:11:33,860 --> 00:11:34,840 I mean, move that up a bit. 191 00:11:35,840 --> 00:11:44,000 Instead, it should be models, template data and this should be models, template data and then in 192 00:11:44,000 --> 00:11:46,100 the handlers, which should have an error now. 193 00:11:48,640 --> 00:11:55,210 So not handlers in where am I rendered render should have an error, you can't be handlers template 194 00:11:55,240 --> 00:11:55,510 data. 195 00:11:55,540 --> 00:12:01,180 It must be models, template data and I can get rid of this at the ID you put in for me. 196 00:12:01,600 --> 00:12:06,670 And I'm not using it yet, but it should at least compile and it should compile. 197 00:12:06,670 --> 00:12:12,070 And one of the thing I forgot to do is here I need to pass in my template data to the buffer. 198 00:12:12,130 --> 00:12:12,510 All right. 199 00:12:12,820 --> 00:12:13,750 So I had two errors. 200 00:12:13,750 --> 00:12:16,040 I put one in on purpose and one that I didn't even notice. 201 00:12:16,570 --> 00:12:18,130 So let's try compiling this again. 202 00:12:23,260 --> 00:12:30,310 It compiled and go back to a Web browser, and now when I load the about page, there is the data that 203 00:12:30,310 --> 00:12:33,630 I've posted and that's exactly what I wanted to have happen. 204 00:12:33,940 --> 00:12:41,590 So I've managed to successfully pass data from my handler to this individual page so that you would 205 00:12:41,590 --> 00:12:42,450 think is the end of it. 206 00:12:42,460 --> 00:12:43,390 But it's not quite. 207 00:12:44,050 --> 00:12:46,650 There are situations, of course, I could do it this way. 208 00:12:46,660 --> 00:12:52,630 I could say every time I'm building a template or rendering a template, I can manually construct all 209 00:12:52,630 --> 00:12:54,930 of the data that I need to pass to that template. 210 00:12:55,390 --> 00:13:01,390 And yet, inevitably, there will be situations where you want certain kinds of data to be available 211 00:13:01,390 --> 00:13:04,960 to every page in the site without adding it by yourself. 212 00:13:05,410 --> 00:13:10,600 So in other words, you want to take a template, data, whatever template that is passed by a handler, 213 00:13:10,930 --> 00:13:16,120 and then add to it data that you want available on every page of your site, which is a pretty straightforward 214 00:13:16,120 --> 00:13:16,600 process. 215 00:13:16,610 --> 00:13:18,660 We may as well do it now just to get it out of the way. 216 00:13:19,210 --> 00:13:26,530 I'm going to do that by coming down to my handlers, my whereas it here, not that one to render. 217 00:13:27,130 --> 00:13:35,650 When I render the page here just before I call that execute function, I'm going to create another function 218 00:13:35,650 --> 00:13:37,170 and I'll put it right above it. 219 00:13:37,180 --> 00:13:46,570 So up here I will call it func add default data and it's going to take one argument and the argument 220 00:13:46,570 --> 00:13:49,870 will be TRD, which is of type. 221 00:13:52,250 --> 00:13:58,850 Points are two models, template data, and it's going to return the same thing, models, template 222 00:13:58,850 --> 00:13:59,150 data. 223 00:14:00,720 --> 00:14:06,480 So that is the function I'm going to call, and right now I don't have any data to add, but I'm going 224 00:14:06,480 --> 00:14:07,740 to just I'll soldiers return. 225 00:14:08,700 --> 00:14:12,920 So all it's doing right now is taking the template data and returning it. 226 00:14:13,290 --> 00:14:19,830 But when I discover to determine exactly what data I want to be available on every page, I can add 227 00:14:19,830 --> 00:14:20,210 it here. 228 00:14:21,150 --> 00:14:27,690 So we come down here and just before I execute that, I simply take I simply say TRD is assigned or 229 00:14:27,690 --> 00:14:32,840 TRD equals add default data and that should work. 230 00:14:33,090 --> 00:14:34,770 So let's try compiling it again. 231 00:14:35,100 --> 00:14:36,270 Stop the application. 232 00:14:36,660 --> 00:14:37,110 Run it. 233 00:14:40,010 --> 00:14:40,550 It's running. 234 00:14:40,670 --> 00:14:42,650 Go to my Web browser, reload the page. 235 00:14:43,040 --> 00:14:45,700 Life is good, no warnings or errors anywhere. 236 00:14:46,130 --> 00:14:49,790 So we're not going to use that ad template, a default data function for a little while. 237 00:14:49,880 --> 00:14:54,980 But it's all set up and easy enough for us to add information to it as needed. 238 00:14:55,340 --> 00:14:55,700 All right. 239 00:14:55,700 --> 00:14:56,530 That's enough for now. 240 00:14:56,810 --> 00:14:58,910 We shall move on to the next section.