Figure out type semantics to use for concatenation and similar cases
Nobody has claimed this yet.
Assessment
- Difficulty
- 5/5
- Estimated time
- Over a week
- Newbie friendliness
- 20/100
Research direction
Start by tracing EF Core's expression-tree type inference and SQL translation for c.CustomerID + i, using the issue's generated SQL as the concrete case. Determine and document the semantics for string length and fixed-length facets, parameter casting, and the resulting expression type; done means the rules are agreed and the translation behavior is covered accordingly.
Written by the indexing model from the issue text.
Description
Suppose we have
var i = 5; //int parameter from closure
c.CustomerID which is mapped in database as nchar(5)
and when you have c.CustomerID + i in expression tree, we try to infer type.
- Should type of parameter i be
nchar(5)?- what if the value does not fit in length 5?
- What should be type of resulting expression?
- It cannot be
nchar(5)because result of concatenation would be larger than that.
- It cannot be
- The translation generates this
[c].[CustomerID] + CAST(@__i_0 AS nchar(5))so we need to figure out exact type to use for casting purposes.
Few ideas around
- Ignore length facets for string?
- Ignore Fixed length too?
- Dominant language
- C#
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Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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