Premise
I had a SharePoint hosted app. In this app, I was querying a List’s item using SharePoint REST API.
Problem
While I had no issues querying items based on a specific query, surprisingly, for certain columns, I was not getting any values. Following is my code snippet that was trying out initially:
executor.executeAsync({
url: "<app web url>/_api/SP.AppContextSite(@target)/web/lists(guid'47f89cf2-359d-4792-9dc4-8da877a5050a')
/getitems
?$select=_x0031_23_x0020__x002d__x0020_Nu,LinkTitle&@target='<host web url>'",
method: "POST",
body: "{ 'query' : {'__metadata': { 'type': 'SP.CamlQuery' }, "ViewXml": "<View><Query><Where><Contains><FieldRef Name='Status'/><Value Type='CHOICE'>in progress</Value></Contains></Where></Query></View>" } }",
headers: {
"accept": "application/json; odata=verbose",
"content-type": "application/json; odata=verbose"
},
success: successHandler,
error: errorHandler
});
Following were the fields I was trying to query above:
- 123 – Number [_x0031_23_x0020__x002d__x0020_Nu]
- Title [LinkTitle]
While I was able to fetch items for the ‘Title’ column, no value was being returned for the first column!
Solution
The issue was that the first column’s internal was beginning with a hex code. This particular issue holds true for any column whose name begins with either a special character or a number. For ex,
- Column with name, Number – 123 was working fine however,
- column with name, 123 – Number was not working.
Now that the issue has been identified, so let’s solve it. 🙂
In SharePoint, if we query fields beginning with a hex code then, we need to prepend, OData_, to the internal name of the field. So now, my url becomes,
<app web url>/_api/SP.AppContextSite(@target)/web/lists(guid'47f89cf2-359d-4792-9dc4-8da877a5050a') /getitems ?$select=OData__x0031_23_x0020__x002d__x0020_Nu,LinkTitle&@target='<host web url>'
Look at the Select System Query Option ($select) for the difference,
$select=_x0031_23_x0020__x002d__x0020_Nu,LinkTitle
became
$select=OData__x0031_23_x0020__x002d__x0020_Nu,LinkTitle
That’s it! Now I can also fetch items from fields whose internal name was beginning with a hex code. 😎
Piyush K Singh 
One follow-up to this: If the field name starts with the underscore character (Category) then you would use OData__Category. You would use 2 underscores after the word OData. Also, notice that you would not be allowed to encode anything. I tried using _x002d in place of one or both underscores and it does not work.
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SharePoint fields can be queried using their internal names only. So, even if the display name is, _Category, I suggest you first check it’s internal name, which, I am guessing might be, _x002d_Category but, you should confirm it once. Now that you know the internal name, just prepend it with OData_.
Also, encoding of _ is _x002d_. Note the trailing underscore at the end. However, you don’t need to guess the encoding/name as its already available.
There are many ways by which you can check a field’s internal name. However, the easiest being, go to List Settings > Right Click on your target field name and select Copy Link/Copy Link Address > Paste it in your notepad. At the very end after the phrase Field=, is your field’s unique internal name.
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Hmm, the website erased the underscore I put in front of Category but I think you get the picture.
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