DynamoDB: ValidationException: ExpressionAttributeNames can only be specified when using expressions

Question

I am writing some code to query Dynamo with a certain filter and I'm using the `expression` package in the Go sdk:

The variable `project` that is referred to is defined in another section of the code. Its string properties `owner` and `name` are not nil/empty.
```
dynamo := dynamodb.New(sess)

filt := expression.Name("projectOwner").Equal(
	expression.Value(project.owner),
).And(
	expression.Name("projectName").Equal(
		expression.Value(project.name),
	),
)

expr, err := expression.NewBuilder().WithFilter(filt).Build()
if err != nil {
       panic(err)
}

queryInput := dynamodb.QueryInput{
      KeyConditionExpression:    expr.KeyCondition(),
      ProjectionExpression:      expr.Projection(),
      ExpressionAttributeNames:  expr.Names(),
      ExpressionAttributeValues: expr.Values(),
      TableName: aws.String("projects"),
}
	
out, err := dynamo.Query(&queryInput)
if err != nil {
       panic(err)
}
```
I get this error:
```
panic: ValidationException: ExpressionAttributeNames can only be specified when using expressions
```
I don't know where it's from or what it means: I *am* using expressions.

Answer

You are confusing between the syntax of `Query` and `Scan`.  
 When building a `Query` command you should use `WithKeyCondition(KeyCond)`:
```
builder := expression.NewBuilder().WithKeyCondition(keyCond).WithProjection(proj)
``` 
and when building a `Scan` you should use `WithFilter(filt)`:
```
expr, err := expression.NewBuilder().WithFilter(filt).WithProjection(proj).Build()
```

DynamoDB: ValidationException: ExpressionAttributeNames can only be specified when using expressions

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