Input validation generating data-* attributes ONLY on Primary key and checkbox type input tags - asp.net-mvc

Question

I've created a sample ASP.NET MVC Core 1.1 web app created using VS2015-Update3. It generates input tags with data -* attributes only on a model property that is a Primary Key, and on a property that is of type bool. For instance, in the following example the generated html (shown below) is showing the data-attributes only on the input tag generated for properties MyEntityId and Prop2 of the model. NOTE: I'm using the default ASP.NET Core Web Application template that automatically installs Jquery, Bootstrap, etc.
Model:
public class MyEntity
{
public int MyEntityId { get; set; }
public string Prop1 { get; set; }
[Column(TypeName = "char(2)")]
[RegularExpression(#"^[0-9]{2,2}$", ErrorMessage = "Must enter two digit numbers"), StringLength(2)]
public string TestCode { get; set; }
public DateTime? StartDate { get; set; }
public bool Prop2 { get; set; }
}
View
<form asp-controller="TestController" asp-action="TestAction" method="post" class="form-horizontal">
<div asp-validation-summary="All" class="text-danger"></div>
<div><input type="hidden" asp-for="MyEntityId" /></div>
<div class="form-group">
<label asp-for="Prop1" class="col-md-2 control-label"></label>
<div class="col-md-10">
<input asp-for="Prop1" class="form-control" style="margin-top:15px;" />
<span asp-validation-for="Prop1" class="text-danger"></span>
</div>
</div>
<div class="form-group">
<label asp-for="TestCode" class="col-md-2 control-label"></label>
<div class="col-md-2">
<input asp-for="TestCode" class="form-control" />
<span asp-validation-for="TestCode" class="text-danger"></span>
</div>
</div>
<div class="form-group">
<label asp-for="StartDate" class="col-md-2 control-label"></label>
<div class="col-md-10">
<input asp-for="StartDate" type="date" class="form-control" />
<span asp-validation-for="StartDate" class="text-danger"></span>
</div>
</div>
<div class="form-group">
<label asp-for="Prop2" class="col-md-2 control-label"></label>
<div class="col-md-1">
<input asp-for="Prop2" class="form-control" style="zoom:0.5;margin-top:25px;" />
<span asp-validation-for="Prop2" class="text-danger"></span>
</div>
</div>
<button type="submit" name="submit" value="testVal">Save</button>
</form>
Generated Html:
<div><input type="hidden" data-val="true" data-val-required="The MyEntityId field is required." id="MyEntityId" name="MyEntityId" value="54321"></div>
<div class="form-group">
<label class="col-md-2 control-label" for="StateName">Prop1</label>
<div class="col-md-2">
<input class="form-control" readonly="" type="text" id="Prop1" name="Prop1" value="TestVal">
<span class="text-danger field-validation-valid" data-valmsg-for="Prop1" data-valmsg-replace="true"></span>
</div>
</div>
<div class="form-group">
<label class="col-md-2 control-label" for="TestCode">TestCode</label>
<div class="col-md-2">
<input class="form-control" type="text" id="TestCode" name="TestCode" value="">
<span class="text-danger field-validation-valid" data-valmsg-for="TestCode" data-valmsg-replace="true"></span>
</div>
</div>
<div class="form-group">
<label class="col-md-2 control-label" for="StartDate">Start Date</label>
<div class="col-md-10">
<input type="date" class="form-control" id="StartDate" name="StartDate" value="2015-10-01">
<span class="text-danger field-validation-valid" data-valmsg-for="StartDate" data-valmsg-replace="true"></span>
</div>
</div>
<div class="form-group">
<label class="col-md-2 control-label" for="Prop2">Test Prop2</label>
<div class="col-md-1">
<input class="form-control" data-val="true" data-val-required="Test Prop2 is required." id="Prop2" name="Prop2" style="zoom:0.5;margin-top:25px;" type="checkbox" value="true">
<span class="text-danger field-validation-valid" data-valmsg-for="Prop2" data-valmsg-replace="true"></span>
</div>
</div>

Answer 1

I'm assuming your issue is that TestCode does not have validation on it, despite having both RegularExpression and StringLength attributes applied. MyEntityId and Prop2 are non-nullable, so there's an implicit required validation for those, while Prop1 and StartDate are nullable and do not have any explicit validation applied. As a result, those are rightly not validated.
TestCode is weird, though. I'm not sure you'd actually get data-* attributes, as both the regular expression and string length can be satisfied using the HTML attributes pattern and maxlength, respectively. But, you should then have pattern and maxlength applied to the input for TestCode which is not the case.
According to the docs, the code you have should work, and at the least, it seems that StringLength is applied via data-val-maxlength rather than (or perhaps in addition to) using the maxlength attribute. There's either some bug at play, or there's something else in your codebase that is preventing the correct behavior from occurring. However, without more code, it's impossible to say.