1 00:00:00,021 --> 00:00:02,040 Okay, just a little bit of practice 2 00:00:02,040 --> 00:00:03,840 with the DynamoDB CLI 'cause there is 3 00:00:03,840 --> 00:00:05,840 some good-to-know parameters that we can use, 4 00:00:05,840 --> 00:00:08,190 and that the exam may ask you questions about. 5 00:00:08,190 --> 00:00:10,830 The first one is a projection-expression, 6 00:00:10,830 --> 00:00:13,460 and this is to specify a list of attributes 7 00:00:13,460 --> 00:00:15,590 that you may want to retrieve from the table. 8 00:00:15,590 --> 00:00:17,690 Maybe you don't want all the attributes from the table. 9 00:00:17,690 --> 00:00:18,880 Maybe you just want a subset, 10 00:00:18,880 --> 00:00:21,720 and so projection-expression is the way to say that. 11 00:00:21,720 --> 00:00:23,600 Also if you want to filter the results, 12 00:00:23,600 --> 00:00:25,430 you can use a filter-expression, 13 00:00:25,430 --> 00:00:28,500 and we'll see how to do both these things into the hands-on. 14 00:00:28,500 --> 00:00:32,040 Now, there are some general CLI pagination option 15 00:00:32,040 --> 00:00:35,400 that includes the DynamoDB and the S3 CLI 16 00:00:35,400 --> 00:00:37,030 but could also include other CLI. 17 00:00:37,030 --> 00:00:40,810 And so, these commands are not just applied to 18 00:00:40,810 --> 00:00:43,160 these two services but to CLI overall 19 00:00:43,160 --> 00:00:44,460 when it returns results, 20 00:00:44,460 --> 00:00:45,890 and they're really good to know overall. 21 00:00:45,890 --> 00:00:50,030 The first one is an optimization which is page-size. 22 00:00:50,030 --> 00:00:52,900 This option is saying that you still wanna retrieve 23 00:00:52,900 --> 00:00:56,030 the full dataset, for example if you're doin' S3 ListBucket 24 00:00:56,030 --> 00:01:00,890 or DynamoDB Scan, but you want each API call made to AWS 25 00:01:00,890 --> 00:01:03,940 to request less data, and maybe a reason 26 00:01:03,940 --> 00:01:07,540 why you would want to do this is to help avoid timeouts. 27 00:01:07,540 --> 00:01:10,360 So by specifying a smaller page size, you will have 28 00:01:10,360 --> 00:01:13,360 more API calls being done, but each API call will return 29 00:01:13,360 --> 00:01:16,720 less data, so it probably will help you avoid timeouts. 30 00:01:16,720 --> 00:01:18,020 We'll see this in a second. 31 00:01:18,020 --> 00:01:19,808 There's also pagination. 32 00:01:19,808 --> 00:01:22,393 Pagination, as the name indicates, is to use pages. 33 00:01:23,272 --> 00:01:25,670 With this, you specify the max number of items 34 00:01:25,670 --> 00:01:28,240 you want to be returned by the CLI, 35 00:01:28,240 --> 00:01:31,330 and you will get a token at the end of this command 36 00:01:31,330 --> 00:01:34,530 called NextToken, and you would pass on that token 37 00:01:34,530 --> 00:01:35,840 to the starting token parameters 38 00:01:35,840 --> 00:01:37,800 for the next command you run 39 00:01:37,800 --> 00:01:41,450 to keep on reading the next page hence the name pagination. 40 00:01:41,450 --> 00:01:43,620 So the first two, projection-expression 41 00:01:43,620 --> 00:01:45,400 and filter-expression, they're only applicable 42 00:01:45,400 --> 00:01:48,720 to the DynamoDB CLI, but all these optimization 43 00:01:48,720 --> 00:01:51,380 and pagination, so page-size, max-item and starting-token, 44 00:01:51,380 --> 00:01:54,350 are applicable to way more CLI in the AWS world, 45 00:01:54,350 --> 00:01:56,310 and you need to know those going into the exam. 46 00:01:56,310 --> 00:01:58,660 So, let's go and have a little bit of practice. 47 00:01:59,550 --> 00:02:01,530 I'm going to use the UsersPost table, 48 00:02:01,530 --> 00:02:03,340 and there's three items in there, 49 00:02:03,340 --> 00:02:04,850 and I'm going to run the queries against those. 50 00:02:04,850 --> 00:02:06,280 So, we have three items. 51 00:02:06,280 --> 00:02:07,840 Two belong to the same user ID, 52 00:02:07,840 --> 00:02:09,580 and we have three different columns, 53 00:02:09,580 --> 00:02:11,970 user_id, post_ts and content. 54 00:02:11,970 --> 00:02:14,220 So, let's go how we can query this table. 55 00:02:14,220 --> 00:02:17,357 Here is my terminal, and I've created a file called 56 00:02:17,357 --> 00:02:20,100 cli-examples that you can just use to run these commands. 57 00:02:20,100 --> 00:02:22,290 The first command I want to show you 58 00:02:22,290 --> 00:02:24,410 is the projection-expression. 59 00:02:24,410 --> 00:02:27,330 If the copy and paste works, here we go, it works. 60 00:02:27,330 --> 00:02:29,940 This projection-expression is saying okay, we'll run 61 00:02:29,940 --> 00:02:33,970 a DynamoDB Scan command on the table name UserPosts, 62 00:02:33,970 --> 00:02:35,890 and I'm running in the region US East one, 63 00:02:35,890 --> 00:02:38,860 so change this if you don't run in US East one. 64 00:02:38,860 --> 00:02:41,210 The projection-expression is saying I only want 65 00:02:41,210 --> 00:02:44,740 to retrieve the user ID and the content column. 66 00:02:44,740 --> 00:02:47,250 No other attributes should be retrieved. 67 00:02:47,250 --> 00:02:49,920 So if I press enter, I'm gonna get my results 68 00:02:49,920 --> 00:02:53,970 of all my items, but all these items, the three of them, 69 00:02:53,970 --> 00:02:57,080 they only returned the content and the user ID. 70 00:02:57,080 --> 00:03:01,060 I did not retrieve from this, the post time stamp. 71 00:03:01,060 --> 00:03:02,450 So, this is a demo into 72 00:03:02,450 --> 00:03:04,550 how the projection-expression can be used. 73 00:03:06,000 --> 00:03:09,690 Next command we want to look at is this filter-expression. 74 00:03:09,690 --> 00:03:11,280 Now, they're really not easy to figure out, 75 00:03:11,280 --> 00:03:12,640 so I'm glad I did. 76 00:03:12,640 --> 00:03:15,690 Again, we run a scan on the same table. 77 00:03:15,690 --> 00:03:17,680 This time we say we want the user ID 78 00:03:17,680 --> 00:03:20,050 to be equal to this value u. 79 00:03:20,050 --> 00:03:20,883 What is u? 80 00:03:20,883 --> 00:03:23,790 Well, you need to specify an expression-attributes value 81 00:03:23,790 --> 00:03:27,740 to say that this u-value is S, which means string, 82 00:03:27,740 --> 00:03:30,170 equals to this value. 83 00:03:30,170 --> 00:03:31,420 What does this value represent? 84 00:03:31,420 --> 00:03:34,250 Well, it represents this user ID right here. 85 00:03:34,250 --> 00:03:37,780 So, it's a little bit tricky to put together this command, 86 00:03:37,780 --> 00:03:41,510 but what it should do is filter our table for the scan 87 00:03:41,510 --> 00:03:44,030 just based on the results for this user ID. 88 00:03:44,030 --> 00:03:47,820 So if I press enter, this time it scanned three rows, 89 00:03:47,820 --> 00:03:51,077 but it returned to me two rows, and the response 90 00:03:51,077 --> 00:03:54,290 of the two rows were the user ID has a value of 91 00:03:54,290 --> 00:03:57,980 string one, two, three usersoi3 so excellent. 92 00:03:57,980 --> 00:04:01,680 So, this filter-expression works as well. 93 00:04:01,680 --> 00:04:05,960 Now, let's get into the page-size demo. 94 00:04:05,960 --> 00:04:09,243 Here, I'm just going to run a straight forward scan. 95 00:04:10,280 --> 00:04:15,270 If I do a scan, this does one API call to DynamoDB, just one 96 00:04:15,270 --> 00:04:18,900 because it tries to return as much data as possible. 97 00:04:18,900 --> 00:04:22,120 But if you wanna do three API calls, we are going to run 98 00:04:22,120 --> 00:04:25,470 this command where we specify the page size to be one, 99 00:04:25,470 --> 00:04:27,730 and by having the page size being one, 100 00:04:27,730 --> 00:04:30,380 we're saying the max number of results I want 101 00:04:30,380 --> 00:04:32,670 from each API call is going to be one, 102 00:04:32,670 --> 00:04:35,140 but because we will still get the full data set, 103 00:04:35,140 --> 00:04:38,420 in the background, it will run three API calls. 104 00:04:38,420 --> 00:04:41,360 If I press enter, as we can see, we still get three 105 00:04:41,360 --> 00:04:45,690 as a final result, but we were issuing three API calls 106 00:04:45,690 --> 00:04:48,810 to DynamoDB because of this page-size argument. 107 00:04:48,810 --> 00:04:53,810 How do we limit the number of results per call to the CLI? 108 00:04:54,030 --> 00:04:56,510 Well, we use the max-items. 109 00:04:56,510 --> 00:05:00,060 If I use this max-item here, I do a scan on the same table, 110 00:05:00,060 --> 00:05:02,370 same region but now say number of items 111 00:05:02,370 --> 00:05:04,960 that I want to be returned at the maximum is one. 112 00:05:04,960 --> 00:05:09,673 I press enter, and here I only get one item back. 113 00:05:10,739 --> 00:05:12,820 And I'm given a NextToken, 114 00:05:12,820 --> 00:05:15,380 and this token is what I should be using 115 00:05:15,380 --> 00:05:20,000 as part of the starting token argument, 116 00:05:20,000 --> 00:05:22,930 and so I'm going to paste the starting token here, 117 00:05:22,930 --> 00:05:25,200 and so here I got the hello world first post. 118 00:05:25,200 --> 00:05:28,170 But if I press enter, now I'm getting my second post 119 00:05:28,170 --> 00:05:30,480 which is awesome new post, second ever, 120 00:05:30,480 --> 00:05:32,410 and I'm getting a new NextToken again, 121 00:05:32,410 --> 00:05:36,460 so we're going to reuse that new NextToken and replace it. 122 00:05:36,460 --> 00:05:41,460 So, let's use this NextToken and paste it here, press enter. 123 00:05:42,843 --> 00:05:45,430 Now, I'm getting new user new post, 124 00:05:45,430 --> 00:05:47,940 and we don't get any new NextToken. 125 00:05:47,940 --> 00:05:50,600 We don't have any new NextToken, so what does that mean? 126 00:05:50,600 --> 00:05:53,020 That means that we are done reading this table, 127 00:05:53,020 --> 00:05:54,750 and there is no more pages to read 128 00:05:54,750 --> 00:05:56,337 hence the name pagination. 129 00:05:56,337 --> 00:05:58,930 That's it, just what I wanted to show you. 130 00:05:58,930 --> 00:06:01,620 It's pretty simple, but hopefully you need to see it once 131 00:06:01,620 --> 00:06:03,730 before you understand how these things work, 132 00:06:03,730 --> 00:06:06,220 so once you remember the structure, look at the code, 133 00:06:06,220 --> 00:06:07,360 try to remember these options. 134 00:06:07,360 --> 00:06:09,100 I think it's really important to understand the difference 135 00:06:09,100 --> 00:06:13,230 between max-items and the starting-token and page-size. 136 00:06:13,230 --> 00:06:14,300 One is for optimization. 137 00:06:14,300 --> 00:06:16,520 The other one is for pagination. 138 00:06:16,520 --> 00:06:17,870 That's it for the CLI practice. 139 00:06:17,870 --> 00:06:18,703 I hope you liked this, 140 00:06:18,703 --> 00:06:20,590 and I will see you in the next lecture.