Why is my CAML query failing when it contains <Query>? - sharepoint

Question

I have a list with a lot of documents (> 5000). I need to retrieve one particular document from it. I use this query:
#"<View>
<Query>
<Where>
<Contains>
<FieldRef Name=""FileLeafRef""/>
<Value Type=""Text"">MyDocumentName</Value>
</Contains>
</Where>
</Query>
<RowLimit>1</RowLimit>
</View>"
And I get a ServerException stating that this operation is forbidden because it goes over the list treshold.
But if I remove the <Query> tag:
#"<View>
<RowLimit>1</RowLimit>
</View>"
It works, and retrieve a single file, which sadly isn't the one I wanted, obviously.
So I'm puzzled here. Why is it behaving like that?

Answer 1

Try
Value Type=File
#"<View>
<Query>
<Where>
<Contains>
<FieldRef Name=""FileLeafRef""/>
<Value Type=""File"">MyDocumentName</Value>
</Contains>
</Where>
</Query>
<RowLimit>1</RowLimit>
</View>"
If you don't like building the query by hand then a couple of good tools are:
- U2U CAML Query Builder which gives you an UI for building the query.
- CAML.NET which is a library for safely building CAML queries

Answer 2

After eventually finding the right keywords to ask Google, I found this question.
The problem is that no field in my library is indexed, therefore when I try to add a query with conditions, all the library has to be read through in order to find the document(s) I need. So obviously, if there is too many documents, I get the exception.
<RowLimit> doesn't prevent this behavior, it only acts on the result of the query.
That being said, there is one field that is automatically indexed: ID. So we can change our query a bit to manually page the documents whose ID are between two values, and simply put the query in a while loop, incrementing the current ID paging each time, like so:
ListItemCollection items = null;
const int paging = 2000;
int currentPaging = paging;
while (items == null || items.Count == 0 || currentPaging < 100000)
{
var query = new CamlQuery
{
ViewXml = $"<View><Query><Where><And><Contains><FieldRef Name='FileLeafRef' /><Value Type='File'>MyDocumentName</Value></Contains><And><Leq><FieldRef Name='ID' /><Value Type='Counter'>{currentPaging}</Value></Leq><Gt><FieldRef Name='ID' /><Value Type='Counter'>{currentPaging - paging}</Value></Gt></And></And></Where></Query></View>"
};
items = list.GetItems(query);
ctx.Load(items);
ctx.ExecuteQuery();
currentPaging += paging;
}
Here's the formatted XML used in the query (query.ViewXml), for better readability:
<View>
<Query>
<Where>
<And>
<Contains>
<FieldRef Name='FileLeafRef' />
<Value Type='File'>MyDocumentName</Value>
</Contains>
<And>
<Leq>
<FieldRef Name='ID' />
<Value Type='Counter'>{currentPaging}</Value>
</Leq>
<Gt>
<FieldRef Name='ID' />
<Value Type='Counter'>{currentPaging - paging}</Value>
</Gt>
</And>
</And>
</Where>
</Query>
</View>