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1 - XPath Advanced
1 +Communication between models
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1 +en
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1 1  {{container}}{{container layoutStyle="columns"}}(((
2 -Within the crash course, we already explained XPath conceptually. In that same microlearning, we also looked at some more uncomplicated cases of using XPath within your transformation. If you need to brush up on that knowledge, please check out this [microlearning](crashcourse-platform-create-transformation-xpath-basic.md). In the intermediate microlearning on this subject, we built upon that knowledge. Please check out this [microlearning](intermediate-create-your-transformations-xpath-intermediate.md) if you need a refresher on that. In this microlearning, we will build upon that knowledge and look at some concrete, practical examples that could be useful in your project.
2 +When your integration landscape grows through time, you might decide to split functional business processes into multiple eMagiz models. In those cases, the question of connecting these models easily, stable, and securely could arise. This microlearning will focus on that question and provide an answer based on our vision and best practices when dealing with the platform.
3 3  
4 4  Should you have any questions, please get in touch with [[academy@emagiz.com>>mailto:academy@emagiz.com]].
5 5  
6 -* Last update: October 25th, 2021
7 -* Required reading time: 6 minutes
8 -
9 9  == 1. Prerequisites ==
10 10  
11 -* Advanced knowledge of the eMagiz platform
12 -* [[XPath Basic>>doc:Main.eMagiz Academy.Microlearnings.Crash Course.Crash Course Platform.crashcourse-platform-create-transformation-xpath-basic.WebHome||target="blank"]]
13 -* [[XPath Intermediate>>doc:Main.eMagiz Academy.Microlearnings.Intermediate Level.Create your transformations.intermediate-create-your-transformations-xpath-intermediate.WebHome||target="blank"]][XPath Intermediate](intermediate-create-your-transformations-xpath-intermediate.md)
8 +* Expert knowledge of the eMagiz platform
14 14  
15 -crashcourse-platform-create-transformation-xpath-basic
16 -crashcourse-platform-create-transformation-XPath-basic
17 -
18 18  == 2. Key concepts ==
19 19  
20 -This microlearning focuses on more complex XPath operations.
12 +This microlearning focuses on communication between two eMagiz models. When communicating to any external party (from the view of a certain model) you should always consider the following:
21 21  
22 -With XPath Advanced, we mean learning that XPath options are complex but could benefit you in your daily work.
14 +* Security
15 +* Loose coupling
16 +* Maintainability
17 +* Clarity
23 23  
24 -Some of the more complex XPath options are:
19 +== 3. Communication between models ==
25 25  
26 -* dateTime calculation
27 -* Filter list
28 -* XPath on JSON
29 -* SpEL notation for XPath
21 +In a low-code platform like eMagiz, you want to prevent using custom scripting as much as possible. However, sometimes in practice, you encounter situations that cannot be realized with the standard toolbox provided within the platform. As a result, we offer the option to use a Groovy script in these situations to achieve the desired solution. In this microlearning, we will look at where you can use a Groovy script and discuss the key considerations when implementing a Groovy script within your model.
30 30  
23 +Most users would think that communication via queues to connect two separate eMagiz models is a smart idea. However, this is something that we do not encourage. We discourage this for several practical and technical reasons alike.
31 31  
25 +When looking at the practical side of things getting it configured correctly is time-consuming and an error-prone action (as is evident by the question). Furthermore, it can lead to unexpected situations in which you make a typo to listen to a queue on which no messages are provided. This queue will however be registered on the JMS level (when you activate the flow in question with the custom configuration) which can lead to confusing queue statistics and even more troublesome false-positive alerting based on missing queue metrics or missing consumers.
32 32  
33 -== 3. XPath Advanced ==
27 +On top of that because you basically allow one model to write and read from queues registered in another model maintaining both models will become very confusing for the ones working on the project at the moment but also for those working on it at a later stage and does that need to provide (incidental) support on the environments.
34 34  
35 -Within the crash course, we already explained XPath conceptually. In that same microlearning, we also looked at some more uncomplicated cases of using XPath within your transformation. If you need to brush up on that knowledge, please check out this [microlearning](crashcourse-platform-create-transformation-xpath-basic.md). In the intermediate microlearning on this subject, we built upon that knowledge. Please check out this [microlearning](intermediate-create-your-transformations-xpath-intermediate.md) if you need a refresher on that. In this microlearning, we will build upon that knowledge and look at some concrete, practical examples that could be useful in your project.
29 +Another practical reason for not wanting this is that we do not actively support this use case from eMagiz. This means that when we do updates to our technical infrastructure we will not take this scenario into account. This could lead to additional work on your part in the future and reduced stability of your solution.
36 36  
37 -Some of the more complex XPath options are:
31 +From the technical point of view, the consequence of this construction is that both models need to know each other certificates and credentials which are not considered secure. On top of that because you, theoretically, can exchange data from any queue to any queue you could create a situation in which updates in one model trigger changes in the other model (i.e. when using the same data model) that are unexpected (and frankly unwanted).
38 38  
39 -* dateTime calculation
40 -* Filter list
41 -* XPath on JSON
42 -* SpEL notation for XPath
33 +We advise using functionality that makes it explicit that both models function independently of each other. From eMagiz we consider two valid alternatives for this:
34 +- Using a web service as a layer of communication between the two models. This web service can be REST or SOAP and has been implemented before
35 +- Using the Event Streaming functionality of eMagiz to write and read from topics.
43 43  
44 -=== 3.1 dateTime calculation ===
37 +Both alternatives have the benefit that the security can be tight and explicit (i.e. only model A can write/post data to model B). Furthermore managing the solution becomes a lot easier as it makes use of the standard functionality within the platform. We have no plans to support this approach in the product.
45 45  
46 -Sometimes we see that a dateTime calculation is needed within a transformation to determine a specific action. As these calculations are not natively supported within the eMagiz platform, you need to use XPath's functionality to calculate the new valid date (or dateTime).
47 -
48 -The XPath standard offers several functions to calculate with dateTime values. The two most used options are dayTimeDuration and yearMonthDuration. With the help of the dayTimeDuration, you can add, subtract, multiple, or divide seconds, minutes, hours, and days regarding the original value. The yearMonthDuration works similarly but then for months and years. An example of such an XPath is: <xsl:value-of xmlns:xs="http://www.w3.org/2001/XMLSchema" select="CDM:StartDate + xs:dayTimeDuration('P1D') * xs:yearMonthDuration('P1M')"/>. In this example, XPath adds one day and subtracts one month from the input date. Note that making this work requires the additional namespace to be defined. Therefore you need a custom snippet within your transformation or a custom transformation to make this work. Furthermore, note that the P1D and P1M could also be filled with the help of parameters to make them dynamic in nature.
49 -
50 -Some examples that we saw during the years:
51 -
52 -* https://my.emagiz.com/p/question/172825635700358186
53 -* https://my.emagiz.com/p/question/172825635700352588
54 -
55 -=== 3.2 Filter list ===
56 -
57 -Sometimes you have a large message which contains a certain list within it. However, logic dictates that you can only send the message if at least one entry in the list for which attribute A is filled and attribute B equals type C. To make that happen in XPath, we first need to navigate to the list within the message. As we previously learned, there are two options to do so. One is to use // to navigate to the entity somewhere in the tree directly. The other is to start at the root and walk the tree from there. In this example, we use the latter. That results in the following XPath example: /root/list[attributeB = 'type C']/attributeA !=''. With this XPath, you filter the list on the specified check and subsequently check whether one of those entries that remains has an attributeA which is filled in.
58 -
59 -=== 3.3 XPath on JSON ===
60 -
61 -With the release of build number .50, we expanded our offering on JSON messages to resemble much of the functionality we previously offered for XML messages. As a result, you can use XPath expressions on JSON messages within the following components (related to XPath):
62 -
63 -* XPath header enricher
64 -* XPath transformer
65 -* XPath router
66 -
67 -To activate the functionality, simply link the JSON source factory support object to one of these components to achieve the desired result. For more information, check out: https://emagiz.github.io/docs/release-notes/build50.
68 -
69 -=== 3.4 SpEL notation for XPath ===
70 -
71 -Sometimes you want to perform an XPath operation but store the header via a standard message header enricher component. As a result, you need a valid SpEL expression to help you in this cause. To do so, you need to know the correct notation for an XPath expression when using the SpEL language. An example of the correct notation is: #xpath(payload,'/root/entity/attribute')
72 -
73 -
74 -
75 75  == 4. Assignment ==
76 76  
77 -Check out which of the XPaths we have discussed today can be found within your project.
78 -This assignment can be completed within the (Academy) project you created/used in the previous assignment.
41 +Consider what your criteria are when communicate between models and compare them to our criteria.
42 +This assignment can be completed with the help of the (Academy) project you created/used in the previous assignment.
79 79  
80 80  == 5. Key takeaways ==
81 81  
82 -Some of the more complex XPath options are:
46 +* Consider the following when communication between two models
47 +** Security
48 +** Loose coupling
49 +** Maintainability
50 +** Clarity
83 83  
84 -* dateTime calculation
85 -* Filter list
86 -* XPath on JSON
87 -* SpEL notation for XPath
88 -
89 -
90 -
91 91  == 6. Suggested Additional Readings ==
92 92  
93 -If you are interested in this topic and want more information on it, please read the help text provided by eMagiz and read more information on the following link:
54 +If you are interested in this topic and want more information, please consult us at [[productmanagement@emagiz.com>>mailto:productmanagement@emagiz.com]]
94 94  
95 -* https://www.w3schools.com/xml/xpath_intro.asp
96 -
97 97  == 7. Silent demonstration video ==
98 98  
99 99  As this is more of theoretical microlearning, there is no video accompanying the microlearning.)))((({{toc/}}))){{/container}}{{/container}}